WATER . In the mythical narratives in which it is frequently employed, the image of water takes on many different aspects. This article shall try to classify its appearances and seek to understand how the diverse functions that it fulfills are ordered.
At the Time of Origins
Many peoples tell how the world, already created in ancient times, was transformed and became what it is now. According to certain Australian traditions, the earth was originally surrounded by water, and in it were many spirits. Through the action of one of these spirits, the earth grew warm, and the first humans emerged from it. According to the Zuni Indians, a complex network of waterways circulates underground; the first Zuni were born there, at the lowest level. A pair of twins created by the Sun then made them climb to the surface. A pond marks the spot where they finally saw the light of day. A northern Australian myth tells the story of a dema (ancestral) deity. After one of his sons struck him with a lance, he threw himself into the sea; there, another of his children drew the lance out of his flesh where it had remained embedded. During the voyage the god then undertook, a spring appeared everywhere he rested. Finally, he plunged into the river Victoria, whose waters he proceeded to stir up until they formed deep branches in the forest; he then disappeared under a rock. From time to time he rises to the surface and causes storms; according to some accounts, he also occupies the region of the rainbow, where rain is formed.
Myths of this type show us water as present in the world from the most ancient times on, but they ascribe to it many different situations. Whether peripheral to the land or underground, water is first a significant element of the universal order. Sometimes it figures simply as a geographical feature—the sea or a river defining the shape of a country. However, there is something more to take note of. Water can be passive, with a spirit independent of it taking the sole initiative in the act of transformation. And yet water is tied mysteriously to the birth of the first humans or to the destiny of a god, who, after disappearing into its depths, remains bound up with storms and rain. The scope of these differences becomes clear when considering lengthier accounts.
In seeking the origin of all things, many peoples relate how water appeared in the course of cosmogonic events. Their explanations fall into three principal mythic systems. According to the first system, the world is created by a god who remains largely transcendent to it. In this case water, like the entire world, is a product of divine action. According to the Desána of South America, "Sun created the universe.… [He] created the earth, its forests and its rivers.… He also created the spirits and water demons" (Gerardo Reichel-Dolmatoff, Desana: Simbolismo de los Indios Tukano del Vaùpès, Bogotá, 1968, pp. 48–49). An African lament evokes "the one eternal God, the creator of the ocean and of dry land, of the fish in the sea and the beasts in the forest" (Louis Vincent Thomas, Les religions d'Afrique noire, Paris, 1969, p. 218).
In the second mythic context, the cosmogony takes on the aspect of a genealogy. The first ancestor is an entity whose simultaneously cosmic and divine attributes appear in the proliferation of his offspring. The waters that are then born throughout the generations are themselves generative. In a Greek system, the ancestral Earth gives birth to Heaven and to Pontos, the realm of the sea, composed of salt water. Earth then couples with each of these male principles. The first of the children she conceives from Heaven is Okeanos, a freshwater river, with deep eddies; he becomes the father of all the springs and rivers. Thus the deity who goes beyond the world remains immanent within it: In a way, he is present in the waters.
Finally, spirit may be presented as one of the primary agents of the formation of the world. Take for instance this Bambara myth: Out of the original void and motion a force, and then spirit, come forth. While the principles of things are being ordered, a mass falls and gives birth to the earth. However, a part of spirit arises; this is Faro, who builds the heaven. Faro then falls to earth in the form of water, thus bringing life to it. Dispenser of life, water is a manifestation of the divine spirit itself.
It is, however, in another type of cosmogony that the breadth and diversity of the functions of water become most intelligible. Here, water symbolizes what existed before the unleashing of the cosmogonic process, or the state of the world in the first phases of its history. There are numerous variations on this theme.
In its fluidity and elusiveness water may suggest the absence of form, the unsubstantiality and confusion from which the world will emerge. Inert, water has no power; a god or other beings independent of water will be the sole agents of creation. For instance, the following tale was told in the Admiralty Islands. In the beginning, there was nothing but an immense sea; in it swam a great serpent. Wanting a place where he could rest, he said, "Let a reef arise!" A reef then arose from the water and turned into dry land.
Biblical cosmogony illustrates the meaning of water in myths of this sort. The Bible brings together various symbols, including the desert, the void and darkness, the abyss, and the mass of water that the abyss contains and above which hovers the breath of God. This divine breath alone signifies reality. The other images have a negative value, evoking the idea of nonexistence; theologians will see in them a symbol of nothingness. Vedic language can go even further:
Neither Non-Being nor Being existed then.
Neither air nor the firmament above existed.
What was moving with such force? Where? Under whose care?
Was it the deep and fathomless water? (Ṛgveda 10.121.1)
In this question, the image of water alludes to the state of things prior to the distinction between being and nonbeing.
Water has no form of its own, but rivers have a bed and the sea has a bottom. This simple fact inspires several myths. Here is a Siberian example:
In the beginning, water was everywhere. Doh, the first shaman, flew over the primordial ocean in the company of some birds. Finding nowhere to rest, he asked the red-breasted loon to dive into the ocean and bring back some earth from the bottom. This the loon did, and on his third attempt, he managed to bring back a little mud in his beak. Doh made of this an island on the original ocean which became the earth.
The original ocean can thus cover some solid element. Moreover, despite its fluidity, water itself has substance; it is itself matter, and may contain suspended matter. In some myths the gods capture this matter or condense it. Thus the Atharvaveda (12.1) reads: "[The Earth] was originally a wave in the heart of the Ocean; the Sages went looking for it with their magic." A Guinean myth tells how Ha made an immense sea of mud and, then, by solidifying the mud, created the earth. According to the Kojiki, Izanagi and Izanami drove a lance into the sea that extended below them. When they withdrew it, the salty drops that fell from it solidified and formed the first land: the island of Onogoro. A Greek commentator on the myth of Proteus expresses himself in more abstract terms:
There was a time when all that existed was formless and muddy … there was nothing but matter that had been spilled out. A formless inertia reigned until the artisan of all things, having attracted order in order to protect life, imposed its imprint on the world. He disjoined the heavens from the earth, separated the continent from the sea, and each of the four elements … assumed its own form. (Heraclitus, Homeric Allegories 64ff.)
In this type of myth, water no longer signifies nothingness; it possesses a true existence. The gods use it, but it remains inert; they alone are active.
Very similar accounts, or even variants of the same myth, however, endow water with a certain spontaneity. This is the case in a story told by the Muskogee of North America. Before creation, they say, a vast expanse of water was the only thing visible, and two pigeons flew over the waves. At one end, they noticed a blade of grass growing on the surface of the waves. From this grass the earth gradually took shape, and at last the islands and continents took on their present form. One may also refer to an Orphic Greek cosmogony, according to which the primordial water appears to have been muddy. The matter it contained was condensed to become earth, and then from water and earth was finally born the mysterious god who would engender the cosmic egg. Despite their very different styles, both of these myths share one feature: Something happens in the original waters, without the intervention of any power external to the waters themselves. They therefore possess a certain intrinsic power. Other myths go on to explain the nature of this power.
In Hindu cosmogonies, waters are often represented as a receptacle of the divine egg or seed, which grows in the waters, carrying the god full of activity. But they do not give birth to what they carry. "In the beginning, he created only the waters, and then, in the waters, he laid his seed. And this became a golden egg.… In this egg Brahmā was born of himself, the ancestor of all living things" (Mānava Dharmaśāstra l.8–9). Auspicious for the development of the divine embryo, such waters fulfill an almost amniotic function. Egyptian mythology has a similar body of water, known as Nun. The primordial water is considered divine. It bears its own name and assumes human attributes. It can speak, and it can form a couple with its feminine double, the goddess Naunet. In Heliopolitan tradition, it is in Nun that the autogenous solar god is born and later rests. There he begins his creative or generative activity, and there, perhaps, the first gods begin their existence.
The image of a vivifying water that favors the birth of a god or the growth of an embryo is in fact very close to that of a fecund and procreative water. Some Egyptian texts give the impression that Nun himself engendered the solar god, whom he calls "my son." Nun has thus been called the "father of the gods." For a more clear-cut example of an image of procreative water, however, one may turn to the Babylonians. The Babylonians recognized two beings, Apsu and Tiamat, who existed prior to the formation of heaven and earth. They are at one and the same time waters, whose currents, in the beginning of time, mingled in a single mass, and two personified divinities, one masculine and one feminine. Their union produces another divine couple, who in turn will have their own offspring, so that Apsu and Tiamat become the ancestors of all creatures and, in this sense, the first authors of the cosmogonic process. Greece had a similar system, which Homer has preserved. Simultaneously currents of water and anthropomorphic deities, Okeanos and Tethys couple and give birth; their descendants will include all beings who will constitute, rule, or people the universe.
Essential to the life of plants, animals, and humans alike, water can be identified with the life-bearing forces and with fecundity itself. The regenerative nature can appear in a less biological fashion. One reads in the Śatapatha Brāhmaṇa (18.104.22.168): "In the beginning, the waters and the ocean alone existed. The waters had a wish: 'How shall we procreate?' They made an effort. They practiced ascetic heating [tapas ], and so it happened that a golden egg appeared." This egg contained Prajāpati. Thus not only is water filled with the desire for procreation (kāma ), it is also capable of truly creative effort and ascetic heat (tapas ).
When looking at the role water plays in the later phases of the creation of the world, one sees these observations confirmed. Within one and the same cosmogonic system, waters can successively assume attributes that enable one to distinguish different systems within the most ancient phases. For example, it was seen that the embryo of Prajāpati developed in the primordial waters. But then Prajāpati himself undertakes the creation of the waters. In the Śatapatha Brāhmaṇa (22.214.171.124–19), Paramestin, son and hypostasis of Prajāpati, wished to become all things on earth. So he became water. Similarly, Prajāpati will become breath, and Indra, the word. These notions are not contradictory; they represent different stages in creation. Whatever their amniotic qualities, the primordial waters are formless and not especially substantive, since Prajāpati still remains an embryo within them. After his birth, however, the god creates more defined and concrete waters outside of himself. In this way the text shows that the deity penetrates the waters just as he penetrates the entire universe.
Other narratives make simpler distinctions among the successive states of water. If primordial waters are an inert mass, it would be logical for them, during the course of creation, to be influenced by the actions of the gods who rule them. In the Bible, God creates a space in the midst of the original waters, dividing it into two masses, the upper and the lower waters. After creating a solid mass, he then separates that from the lower waters, thereby forming the sea and dry land.
Waters also submit to the demiurgical action in more ambiguous accounts. Here is a Fali (African) myth: One of the first animals, the tortoise, gave the world its first structure by laying out a ditch on the waters. After the first crisis, when rain threatened to submerge all things, the toad—another of the first animals—completed the structure. He separated standing water from running water and opened up a second path for the waters, cutting through the earlier ditch. Thus he divided the world into four parts.
Passive waters can also be mere instruments in the hands of those who confront each other in the course of great cosmogonic battles. In Hindu mythology, the demon Vṛtra holds back the waters and prevents them from irrigating the earth. Indra, who is waging a difficult war against him, is finally victorious and gives life to the world by releasing the waters. Mesopotamian myths are more complex. When the god Enlil decides to destroy humanity, he first holds back the rains and prevents underground waters from reaching the surface. Then, in a second attempt, he unleashes the waters, causing a flood.
Although waters thus appear to be temporarily mastered by the gods who use them, they are not completely inert. Not only do they seem to help Indra in his combat, but they are used by the gods primarily because they have a power of their own. The gods retain them because they are fertilizing; they unleash them because they are destructive.
The life-bearing and generative qualities that have been recognized in some of the primordial waters become manifest in the later phases of the cosmogony. Thus in a later stage of the Sumerian cosmogony, Enki, the Sumerian water god, impregnates Nintur, a goddess close to the earth, by scattering his seed on a riverbank; he then becomes the father of the goddess Nimu. With Nimu he begets Ninkurra, and with Ninkurra, Ottu. Similarly in Greece, whether they be the primordial pair (as in Homer) or be born of Heaven and Earth (as in Hesiod), the river Okeanos and his spouse Tethys have many offspring in the form of springs and rivers; the latter also procreate. In this manner waters contribute to the growth and enrichment of the universe. They also do so in another way: Enki fills ditches, canals, and fallow land with water, thus participating in the organization of the world.
Amma, the Dogon creator god, also has close affinities with heaven and water. His children, the snake-shaped Nommo, who are associated both with water and with the primal word, are the most active and successful agents of the cosmogonic impulse. They contribute to the birth of sexuality and permit the birth of the first ancestors. The latter, who in turn acquire the dignity of Nommo, keep close ties with water. After eating the first dead person, one of them furnishes society with the principles of its structure by vomiting up water—a prefiguration of torrents and ponds, the source of the five rivers, and of the waters of parturition.
Finally, water is sometimes tied more specifically to the birth of humanity. A trout out of water couples with a man from the underground lakes to beget the first clans of the Desána. According to some New Guinea traditions, the dema deities once lived under the earth, except for one of them who dug a hole in the ground. The others came out through the hole; then it filled up with water, and fish began to swim in it. After a complex sequence of events the fish became men. Finally, in Greek mythology, men often appear by coming out of a river.
One may now consider instances in which waters are portrayed as destructive. Several examples can be found in the ancient Near East. The Ugaritic Baal, god of the storm and of rain, symbolizes the forces of life. He periodically struggles against Mot, the incarnation of drought and death. He must also combat and conquer Prince Yamm, that is, the sea prince. Because of the gaps in knowledge it is difficult to locate this conflict within the mythical history of the world. So much, however, is certain: Yamm is threatening, and Baal's victory is necessary to the survival of the universe.
Things are clearer in the Enuma elish. Troubled by the proliferation and activity of their offspring, Apsu and Tiamat, whose mingled waters had given birth to the most ancient beings of the Babylonian myth, one day tried to destroy their descendants. Apsu, who was the first to try, was quickly conquered by Ea's magic. Ea then built his temple on the waters of Apsu, which were henceforth underground. Tiamat, who tried next, was more formidable, but was killed in the end by Marduk. By blowing into and swelling up the monstrous body of Tiamat, the young god separated the celestial waters from the earth; he opened the way to mountain rivers as he imposed his order on the entire universe. The primordial beings thus appear to want to abolish the agitation that accompanies the rise of the world in order to recover the peace they knew in the undifferentiated state of the first ages. Their inertia proves destructive. Tiamat appears as a monster in the army of monsters she has raised. The original divine waters must be conquered before the organizing gods can accomplish their work by pushing them back to the ends of the world.
Water in the Present World
One again encounters the different qualities, functions, and powers of water when looking at the position it holds in the completed world. Waters are one of the great domains of the ordered universe. Evoking the totality of the world, an Egyptian tale lists the sky, the earth, the domain of night, the mountains, and the waters. The Ṛgveda refers more simply to the sky, the waters, the earth. But despite such seemingly straightforward classifications, water is not thereby reduced to its palpable appearance; it continues to occupy places that are inaccessible to us; it possesses unsuspected qualities and powers.
The cosmic waters
For many peoples waters constitute the limits of the universe. They make up a vast expanse, in the middle of which lies the earth, like an island. They may be divided into two oceans on either side of the world, or they may flow in a river that surrounds the world, like the Greek Okeanos. They also frequently occupy the lower regions of the world in a more or less complex network of waterways underground. Or again, sometimes the entire earth is believed to rest on water. Finally, water is also found in the upper regions, above the heavens. Thus water can surround the world in any of the three dimensions of space. For the Desána Indians, a region bathed in water extends under the earth; water also circulates in the filaments of the Milky Way. In Mesopotamian texts the earth is built on the waters of Apsu, while the waters of Tiamat occupy the space above the heavens.
Waters can also help to define the center of the world. According to the Fali myth already cited, this center is located at the intersection of two open trenches in the waters. A character from an Iroquois myth runs around a lake to make the earth grow; the earth then develops on all sides under his steps. The great Ugaritic god El dwells at the source of the rivers in the midst of the course of the two oceans. The Guaraní Indians call the original abode of their ancestress the "Gushing Spring." It is the true center of the earth, the true center of the land of their first last father.
Because they occupy highly significant parts of the universe, waters help to define cosmic order. The Śatapatha Brāhmaṇa says categorically: "The waters are the order of the world" (126.96.36.199). In particular, bodies of water often establish important boundaries. In one widespread image, a lake or river separates the land of the living from the world of the dead. Examples of such a body of water include the river one crosses to reach the Babylonian Land of No Return and the Acheron of the Greeks. Furthermore, just as one must cross the waters to enter the realm of death, one must also cross the waters to enter the land of the living; according to the Ewe people, a child crosses a river when it is born.
Not all peoples make an explicit relationship between cosmic waters and the waters nearer at hand. Several do, however. Thus rains are sometimes believed to come from the celestial waters, and rivers from waters underground, if not from the waters surrounding the earth. Some texts provide more complex images. In a Babylonian poem, springs and rivers arise from the head of Tiamat's corpse; they therefore seem to come from the waters that occupy the upper regions of the world, even if these are near the earth, at the ends of the horizon. In ancient India, the Ganges was thought to descend from the heavens.
Waters and the divine
Wherever they are found, waters are often bound up with divine powers. The Hindu world generally holds them to be goddesses. More explicitly, in other cases, it is the sea, certain rivers, and certain springs that are considered to be gods. People in Vedic India, for instance, sacrificed to rivers. The Tigris and the Euphrates appear in a list of Hittite deities. Rivers are invoked in one Homeric oath.
There is something remarkable about these water deities. They are something more than representations of a purely natural element. Thus while the Egyptian Nun is a waterway on which the boat of the Sun sails at night, he is also a personage who can speak. Similarly, the name of the Ugaritic god Yamm means the sea itself; another of his names evokes the image of a river, but he also appears with the features of a prince or judge who sends ambassadors to the divine assembly. The Greek Pontos is the salty expanse of the sea; he is also a masculine being who couples with Earth and sires offspring. In Egypt, the Nile (and its floodwaters) is honored as Hapi, an anthropomorphic god. Water is thus the manifestation of a divine power that does not exactly coincide with the tangible appearance of the liquid element. Nevertheless, its immanence within this element is such that water can be perceived as the divinity itself.
In other cases, however, waters simply serve as the abode of spirits or sacred powers. Such spirits may inhabit a lake, a river, or the waves of the sea, or like others may live in a grove, a rock, or a mountain. Several gods that exercise a more extended authority should be mentioned separately. First of all, there are lords of rain, who are in some sense believed to cause it. However, rain also depends on beings whose powers are not restricted to the control of rain. In order to obtain rain, therefore, one must invoke several gods together, or certain ancestors who have become powerful spirits. Rain is sometimes conceived of as a gift from the supreme being, or the god of rain may be made into the supreme being itself.
Several ancient Mediterranean and Near Eastern peoples had a storm god. He rides or gathers the clouds, causes thunder and lightning to strike, and makes the rain fall. This storm god occupies a preeminent position among the gods; he can reign over them, protect the cities or their kings, and extend his power over the entire universe. Less prominent in the Hindu pantheon, the storm god Parjanya is a destroyer of demons; in some texts, he seems to be in command of the whole world.
The power of the gods that reign over the waters in a more general fashion is similarly extensive. The Sumerian god Enki, who comes by sea from a faraway land, established his residence or temple on the underground waters of Apsu, whom he has subdued. Enki is the lord of the waters. After being the major organizer of the world and one of the creators of humanity, he remains the master of fate. Along with An and Enlil, he belongs to the supreme triad. The same can be said of Ea, his Akkadian counterpart. King of the abyss, god of the vast sea, lord of the terrestrial waters, Ea has his place in the celestial world, and his counsel is heeded by the gods. Thus the power of the god of water usually transcends the domain of water.
The inverse phenomenon is also found. The authority of a more universal god is exercised in privileged fashion on the aquatic world. In the Veda, for example, Varuna is a major god who rules over nature, gods, and humans; he is the guardian of ṛta, the religious order of things. He is often closely linked to water. With Mitra, he can cause rain; with Indra, he can declare: "It is I who have swelled the rushing waters" (Ṛgveda 4.42). He rests on the waters, and his golden house is built on them. The two oceans are his entrails; he is hidden in each drop of water.
The situation is more highly defined in Greece. Poseidon, the god of the sea, is not essentially an aquatic deity. His name and several myths prove that he has close affinities with the earth. Son of the ancient king Kronos, he was given sovereignty over the seas when the paternal heritage was divided up; one of his brothers got the netherworld and the other, the heavens. Thus he commands the waters and raises tempests, but he is not immanent in them. Other gods—Pontos, Nereus, and Proteus—are more intimately tied to water. But in the case of Poseidon, sovereignty originates in a region beyond the domain where it is exercised. Whatever their wealth and power, waters are not the source of a political type of power. Political power is closer to the heavens; this is why it cannot be held by a god of the storm.
The qualities and powers of water
In their varied manifestations, the water gods and the waters themselves possess in the present world qualities or traits comparable to those that have been seen in the primordial cosmogonies. The waters that extend beyond the world and delimit it may in some cases be a symbol of the void, as they once were of nothingness; but this is not certain. These faraway waters sometimes feed terrestrial waters: They must have the same density. Water's fluidity and elusiveness are, however, manifested in the faculty of metamorphosis found in certain aquatic spirits or divinities. In a Vietnamese tale, a water spirit takes the shape of a seductive boy. Hindu nymphs turn into birds, and Greek sea gods, Proteus, Nereus, and his daughter Thetis, assume several forms in succession to escape those who attempt to detain them. This ability can be transferred. In Burmese narratives, the water of a certain pond transforms the person or animal who drinks it, the former into an ape, and the latter into a human.
Water is essential for human life; it ensures human nourishment by fertilizing the land. It is more than nourishment, because it is the source of nourishment. It may, therefore, be compared not only to milk, but more particularly to the cow. Because of its utility, it is perceived as a privileged support of vital forces. The Vendas, for instance, equate water with the blood, while the Desána view the rivers as umbilical cords joining people to the amniotic waters underground. In both Hindu and African texts, it is common to speak of the waters giving life and engendering humankind.
This is why water is found associated with sexuality. The Diola sing: "Women's sexual organs are full of water …, if Ata Sembe sleeps with a woman, he will always get her pregnant" (Louis Vincent Thomas, Les religions d'Afrique noire, Paris, 1969, p. 202). In this respect, waters often assume a feminine character. The Apsarasas of India and the Greek Naiads and Nereids are young women, caught up in erotic adventures. But the waters can also be masculine. "They rest on sperm, as Varuṇa rests on the waters," says the Bṛhadāraṇyaka Upaniṣad 3.9.22. To the Greek poets, the heavens send rain, like seed, to the earth, in an amorous outburst. The Egyptian god of the floodwaters of the Nile—Hati, the dispenser of life—is androgynous, and the Nile is imagined as half man and half woman. Its waters are male, and its arable land is female. Together, they are father and mother. In Greece the rivers are strongly masculine, and like the gods of the storm and of rain, have the attributes of a bull.
As vital principle, water allows people to ward off illness and to keep death away. Because water makes the plants of the pharmacopoeia grow, or because of the effects of its intrinsic qualities, the Veda associates it with the origin of medicine. In particular, water is believed to be highly effective against the venom of snakes. In a more positive sense, water is said to give vigor, make old men young, and prolong life.
Water is even capable of conferring immortality. Gilgamesh finds the herb of life, which enables people to escape death, at the bottom of the waters. Several peoples speak of a "water of life" that bestows immortality. Similarly, to give her son Achilles eternal life, Thetis wants to plunge him into the waters of the Styx. The Greeks in general establish a relationship between Okeanos and ambrosia, as the Indians do between water and soma.
There is a more enigmatic aspect of water: It possesses wisdom and knowledge. Water seeks the truth, one reads in the Vedas. The Mesopotamian water god Ea, full of wisdom, dispenses counsel to the gods. As a sage, he protects the mythical old wise men who were born in the abyss in the form of fish. The most ancient Greek water gods engender daughters whose names denote qualities of intelligence. Among the Oceanids, these are Metis ("prudence") and Idyia ("the knowing one"); among the Nereids, Panopeia ("the all-seeing one") and Nemertes ("the veracious one"). The latter, says Hesiod, has the same quality of spirit as her father. Nereus is in fact frank, loyal, and gentle, always concerned with justice. He resembles Proteus, who knows the present, the past, and the future.
Where does this wisdom of water come from? A Guaraní narrative establishes a relationship between the freshness of water and the freshness of the soul accompanied by moderation. In a Vedic text the waves, which stave off all evils, also keep away lies. A Greek text associates the extent of knowledge with the immensity of the depths of the sea. But perhaps the wisdom of the water gods is a function of their age. In the Hellenic world, the wisest among them are called "the old men of the sea."
Waters, which at one and the same time are sages and generative forces—to the point of symbolizing at times the creative power itself—are close to the word. To the Dogon, water and the word are joined in the person of the Nommo, whose civilizing activity simultaneously links the arts of civilization with the word and with wetness; one finds similar associations among the Bambara. In Ṛgveda 10.125, the ritual word itself, whose efficacy is cosmic, says of itself: "My origin is in the waters, in the ocean." Water is not always beneficent, however. In the present world, water can be hostile to humans, just as it could be destructive in the remote time of myth. There are catastrophic rains and floods; people drown in rivers and seas. These are not simply accidents but the manifestation of evil powers allied with the liquid element. One example alone illustrates this: Indigenous peoples of the north of Australia have a serpent-shaped spirit that lives in the clouds during the dry season and in marshes during the rainy season. It is he who drowns humans in floods, he who swallows them up when they venture out into swamps.
The negativity of water can take other forms. For the Desána, water is a symbol of illness. In one Mesopotamian text, bad coughs are caused by Apsu. An account from Gabon goes even further: The water spirit embodies rain, cold, and death. Mesopotamia also has waters of death, just as it has waters of life.
This hostile power is sometimes incarnated in monstrous creatures. The Desána believe that a formidable centipede lives in the sea; they also talk of maleficent serpentine creatures, some of whom eat children. The descendants of Pontos, the Greek god of the sea, include several hybrid beings with destructive powers, such as the Gorgons, who dwell near the waters of Okeanos, and the Hydra, in the marsh of Lerna. One recalls that Tiamat took on the form of a monster. Such monsters survive in the beliefs of ancient Israel; they are the leviathan, Rahab, and the dragon Tannin.
In the Hebrew scriptures, the ocean itself is often represented as an adversary of Yahveh. Of course, in imposing his order on the world, Yahveh conquered the waters and subdued the monsters they harbor; he is henceforth their master. However, their menace continues; the sea monster might reawaken, and if he does, God, who watches him, will kill him.
At times beneficent and at others maleficent, close to the principles of life and to creative power but nonetheless capable of destruction, a relative of gods and monsters, water bears within it all the ambiguities of the sacred. It is an agent of purification not only because it bathes, dissolves, and carries off material filth; its cathartic power is even more mysterious. According to a Babylonian text, water banishes all evils, even those that have not yet had an impact but that have been foretold by bad omens. In a Vedic hymn, water frees humanity from the consequences of false oaths and from all the sins people have committed.
The purity conferred by water is a positive trait. Water conveys to humankind certain of its virtues. It causes vision, according to a Vedic text. In a Greek legend, Pherecydes predicts an earthquake after drinking some water from a well. When Okeanos and Tethys purify Glaucus, they render him capable of undergoing the deification process to which he is subject. Thus, waters are fully purifying to the extent that they are also, to a certain extent, sacralizing.
Several of the qualities of water just discussed are manifest in the world of the dead. For certain Zuni societies, the ancestors inhabit a village at the bottom of a lake. The members of the society believe that when they die they will go to sleep and wake up as young children in this village, at the bottom of the "whispering waters." These waters seem to be the symbol of a blissful condition where ancestral life and childhood commingle. The beliefs of the Desána go even further. A region bathed in water, Axpicon-dia, extends beneath the earth; from there came the first organizer of the world. It is a uterine domain, the source of all life, to which the people yet to be born are tied by a sort of umbilical cord. The best of the Desána will go there after death. Happy death is thus conceived as a return to the amniotic waters. Among the Polynesians, the dead inhabit a sad region, located beyond the seas; the chiefs, however, go to a different land, where the god Tane gives them a water of life that brings them back to life.
Nun, the primordial water, crosses through the Egyptian land of the dead. At night, the boat of the sun sails over its waves to the east. In some texts, the dead board this boat and make its journey with it. In other texts, they bathe in Nun, into which the sun god also dives. Assimilated to him, they come out again, regenerated. But the infernal waters are not always beneficent and life-giving. They contain reefs that the ferryman's boat must steer clear of; they contain dangers and are disquieting. The Nun was supposed to be the site of mysterious drownings.
Among the Greeks, Hades contains rivers and lakes. The names of two of these rivers reveal their nature: Pyriphlegethon (Puriphlegethōn ) means "burning and flaming like fire"; Cocytus (Kōkutos ) means "groan, lamentation." The rivers terminate in the abyss of Tartaros where, according to Plato, evil souls suffer a temporary punishment. Other souls, however, purify themselves on the banks of the lake Acherousias, where they pass before reincarnation. Proclus states more clearly that the souls purified in Acheron attain a better fate.
One frequently recurring idea is that the dead are thirsty. Drink refreshes them; thanks to it, they regain some form of life, as suggested by Egyptian texts. Not all waters, however, are equally beneficent to the dead. In certain Greek traditions, there are two springs in the netherworld; the initiate knows he must drink from the one that comes from the Lake of Memory. Plato mentions a Plain of Forgetfulness where the Lake of Negligence is found. One of the infernal waters thus suppresses memory while the other maintains and reaffirms it, acting like the water of wisdom and knowledge already discussed. The importance of this opposition is apparent in the privilege granted to Pythagoras and Empedocles, who were said to have been allowed to retain the memories of their previous existences. It would appear from a reading of Empedocles that this privilege belongs to the souls who will shortly escape reincarnation.
In conclusion, the wide range of meaning given to the image of water is not without limits, and even opposing meanings given in different myths are not incoherent. These diverse meanings are in large part suggested by the diversity of human experience of water as a natural phenomenon.
Water can be ambiguous. As a fluid, it can symbolize a pure absence or an as yet still amorphous material that will be used by the gods. It may fulfill a positive function. It bathes, dissolves, and purifies. Essential to human life and necessary for the growth of plants, it symbolizes a generative or life-giving quality, very similar to creative power. It is thus divine and sacralizing. Yet it is also capable of playing a negative role. The gods can utilize the destructive power of its waves. Active in itself, whether divine or monstrous, water erodes everything that takes form and tends to annihilate all distinctions in its own inconsistency. Finally, just as rivers and seas contribute to defining the contours of a country, so the dividing of the waters helps to define cosmic order.
The image of water therefore is not univocal. It can never be interpreted without considering the totality of the myth in which it figures. But it is not indifferent, defined only by the position it holds in the mythic system of a given society. Capable of calling forth the memory of various concrete experiences and numerous emotions, it carries specific meanings within it in a potential state. Each narrative actualizes some of these meanings.
No rule of logic requires that the meaning that water assumes in the evocation of the time of origins must remain unchanged during the course of the cosmogonic process or in the present world. On the other hand, in the small number of mythic systems that this author has studied in some depth, it has been striking that the uses of the image of water, often quite diverse, nevertheless remain coherent, owing to the theological intention that inspires the whole of a given system.
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Jean Rudhardt (1987)
Translated from French by Erica Meltzer
Because of its scarcity, water plays a central role in Middle Eastern politics and society.
Nowhere in the world is water more important than in the Middle East and North Africa. In no other region do so many people strive so hard for economic growth on the basis of so little water: here is found 5 percent of the world's population but only 1 percent of its fresh water. Of the ten nations with the least water per capita, six are in this region. No wonder that both Jewish and Muslim scriptures are full of references to water.
Role of Climate
The more heavily populated parts of the Middle East are semiarid, with rainfall of 10 to 29 inches (250 to 750 mm) per year. However, low rainfall is less of a problem than variability in rainfall. The great bulk of the rain falls in four winter months, with none falling during the rest of the year. Rainfall also changes rapidly with distance, from more than 20 inches (500 mm) on the coast of Lebanon to 8 inches (200 mm) in the Biqa, only an hour away by road but across the Lebanon mountains.
Seasonal and spatial variations in rainfall are sharp but predictable. What makes planning difficult is the sharp variation from one year to the next. Reliable flow in the rivers (the flow that can be expected nine years out of ten) is only 10 percent of the average. In northern latitudes, water planning can be built around statistical averages; here, it must be built around extremes.
This already difficult water situation will likely get worse. Population growth rates are high, and most climate change models suggest higher temperatures, lower rainfall, and more frequent droughts for the region.
Role of History
Development in the Middle East and North Africa has always been more dependent on water than on any other resource, including oil. By the fourth millennium b.c.e., the Sumerians had built a paradise in what is now Iraq through intricate canals for irrigating crops; two millennia later it had largely collapsed because of salinization of the soil. Ancient cities, such as Palmyra in Syria, were possible only because of carefully engineered tunnels, called qanats (foggaras in Iran), to bring water from springs tens of kilometers away.
Over the years, the peoples of the Middle East have made water a preoccupation, and each nation has a central agency, typically a full ministry, to deal with water. Many of the principles for good water management were worked out in the Middle East—although just as often they were ignored for political, financial, or social reasons.
The Middle East includes two of the mightiest river systems in the world. The Nile has two main branches: The White Nile originates in Uganda, and the larger Blue Nile (together with the Atbara) originates in Ethiopia; they join near Khartoum and flow northward through Egypt to the Mediterranean. The Tigris and Euphrates both originate in Turkey and flow south-southeastward through Syria and Iraq before joining and flowing into the Persian Gulf via the Shatt al-Arab, at the Iranian border.
The region also includes numerous mediumsized rivers, such as the Jordan, which flows from three springs through the Sea of Galilee (one of the few natural lakes in the region) and into the Dead Sea, 415 meters below sea level. Only Turkey has an
abundance of river water, but its big rivers are only found in the eastern part of the nation. Finally, there are small coastal rivers (many of them ephemeral), and a few major wetlands, such as the marshlands in southern Iraq and the Sudd swamp in southern Sudan.
The construction of new dams and pipelines to deliver water from major rivers in the Middle East will cost two or three times as much per unit of water as current supplies, and if construction occurs in upstream countries, such as Ethiopia and Turkey, it will reduce flows downstream. Therefore, the region will increasingly shift toward the use of underground water, which has the great advantage of not evaporating. (Lakes and reservoirs in the region lose meters of water per year to evaporation.)
Historically, underground water was tapped by shallow wells dug in unconsolidated materials to get small flows of water. Today, much larger volumes of water are extracted from wells drilled tens to hundreds of meters into aquifers, which are rock layers with pores that contain water. Renewable aquifers are replenished (generally slowly) by rainfall; non-renewable, or fossil, aquifers contain water trapped in sediments laid down millions of years ago.
Just more than 10 percent of the water supply for the region comes from aquifers, but in Israel and Jordan the share approaches 50 percent, and in Kuwait and parts of the Arabian Peninsula it approaches 100 percent (apart from desalination). Libya's Great Man-Made River pumps water from fossil aquifers in the south of the country and moves it 930 miles (1,500 km) to farms and cities in the north.
The third most important source of water in the Middle East is recycled sewage, which is treated and reused, mainly for irrigation. Despite common
belief (shared by both Muslims and non-Muslims), there is no objection in Islamic law to the reuse of sewer water provided it is properly treated.
More than half of the world's desalination capacity is found in the region, mainly in the oil-producing nations of the Arabian peninsula with lots of by-product natural gas that was formerly flared. (Desalination is an energy-intensive process.) Costs for desalination have fallen to a level that makes it feasible as a source of potable water but still too expensive for irrigation.
Other sources of water are individually small but collectively provide sizable amounts of water. Water harvesting gathers rain that falls over a wide area and directs it to one field through small channels and micro-barrages. The technique can allow crops in areas where rainfall is only 4 inches (100 mm) per year. Rainwater is also collected from rooftops and stored in cisterns. If handled carefully, rooftop water can be used for drinking.
Uses of Water
By far the largest share of water in the region goes to agriculture—as much as 90 percent of total water use in some countries, and 60 percent in the more industrialized countries.
Drinking requires only a relatively small volume of water, but it must meet higher standards than that used for irrigation. Thirty liters of potable water per person-day is generally regarded as the minimum for drinking, cooking, and washing.
Industrial water use is low. Food and beverage processing are the largest industrial consumers. More is withdrawn for cooling but most of this water is recycled or returned to the watercourse.
A hidden but critical amount of water must be left in place to support fisheries and hydropower, as well as to protect habitat. This use is typically neglected by governments when they drain swamps, canalize rivers, or extend land. As a result, not only has the environment been degraded, but fish catches have declined and the salinity of groundwater has increased.
The nations of the Middle East all face three overlapping sources of stress in their water management: 1) quantity, which has been a source of stress since history began; 2) quality, which is a newer stress but increasingly important; and 3) equity, which occurs when the same water is subject to competing demands.
Quantity. Iran, Iraq, Lebanon, Sudan, Syria, and Turkey are fairly well endowed with water, with more than 1 million cubic meters (Mcm) per capita; Algeria, Egypt, Israel, Morocco, and Palestine form a middle group; and Jordan, Libya, Tunisia, and the countries of the Arabian Peninsula are least well endowed, with less than 500 Mcm per capita. However, water availability is declining in every nation, which means that current patterns of water use are not sustainable. Some projections for the Jordan River basin suggest that by 2025 household and industrial uses will require all the fresh water, leaving none for farmers. Most nations are also drawing down their renewable aquifers and mining fossil ones. Some have annual water deficits of several thousand Mcm.
Water quantity problems in the region can be resolved in small part by exploiting additional
|estimates for 2000|
|country||total||per capita||use (%)||domestic||industry||% with safe (cubic m/p) drinking water|
|* percentage by sector adjusted by author on basis of estimates by the planning department of the israeli water commission. all data for israel based on estimates by the author.|
|source: Gleick, Peter, et al, ed. The World's Water: The Biennial Report in Freshwater Resources, 2002–2003 (Washington, D.C., Island Press, 2002).|
|table by ggs information services, the gale group.|
sources of supply but in much larger part by better use of the water that is already available. People in the region use less water than those elsewhere in the world, but as a result of poor management and misguided economic policies conservation here (as in most other parts of the world) remains far short of its potential. Many nations lose half the water put into municipal systems to leaks, and they typically deliver piped water at low (or no) price. Cost-effective savings of 25 to 50 percent are possible in most uses.
Moreover, every country in the region provides water to farmers at highly subsidized prices. Under the influence of higher prices, Israeli scientists developed drip irrigation systems that have cut water use per hectare by 40 percent. However, drip irrigation is expensive and not appropriate for all crops. Lower-cost sprinkler systems, used at night to minimize evaporation, can also increase irrigation efficiency, as can irrigating only at times critical to plant growth.
Most analysts find that water is tens of times more valuable in industrial or household uses than in agriculture. Therefore, crops grown in the region will gradually be replaced by imports. It takes roughly a thousand tons of water to produce one ton of wheat. Using that ratio, Middle Eastern nations already import grains with a virtual water content equal to the flow of the Nile.
Quality. Much of the limited fresh water in the Middle East is polluted from growing volumes of human, industrial, and agricultural waste. Three problems stand out: 1) Overpumping of wells causes a decline in the water table—by as much as a meter a year in some areas. This decline adds to pumping costs and permits lower-quality water (or, if near the coast, seawater) to flow inward and contaminate the aquifer. The only way to avoid the problem is to match pumping rates to inflow. 2) Agricultural runoff is the major non-point source of water pollution—mainly sediment, phosphorus, nitrogen, and pesticides. Better farming methods, such as conservation tillage, contour planting, and terracing can control soil erosion and cut pollution by half or more. 3) Urban sewage systems have either begun to deteriorate or cannot handle the growing loads placed on them. Large investments are needed to improve their physical infrastructure.
Equity. Most of the larger rivers in the region cross an international border—some cross several borders—or form a border. No tabulation exists for aquifers that underlie national borders, but there are many.
Despite many statements suggesting that the next war in the Middle East will be over fresh water, there is little evidence for this. Not a single war has been fought over water for hundreds of years, but many treaties dealing with water have been signed. Water will be a source of conflict, but the conflicts will mainly be intranational rather than international. Likely sources of conflict include rural and urban users contending for the same water and rising demands from poor farmers, who are often disadvantaged in their access to water, and from women, who typically want more water for their households while men prefer to use it to grow cash crops. Israeli control of water in the West Bank is contentious, but even here experts have shown that compromise is feasible.
None of the three stresses on water in the Middle East will be easily resolved. Most of the nations in the region have already reached or are fast approaching the limits of their indigenous water supplies. Although higher prices for water and technological advances may defer the crisis, the only long-term solutions involve much greater efficiency in use, full reuse of wastewater, and gradual shifts of water from agriculture to other sectors. All of the nations of the Middle East and North Africa must revise their water policies to provide for a sustainable future, and they must find equitable ways to share water within and between nations.
Amery, Hussein A., and Wolf, Aaron T., eds. Water in the Middle East: A Geography of Peace. Austin: University of Texas Press, 2000.
Beaumont, Peter. "Water Policies for the Middle East in the Twenty-first Century: The New Economic Realities." International Journal of Water Resources Development 18, no. 2 (2002): 315–334.
Brooks, David B., and Mehmet, Ozay, eds. Water Balances in the Eastern Mediterranean. Ottawa: International Development Research Centre, 2000.
Kolars, John. "The Spatial Attributes of Water Negotiation: The Need for a River Ethic and River Advocacy in the Middle East." In Water in the Middle East: A Geography of Peace, edited by Hussein A. Amery and Aaron T. Wolf. Austin: University of Texas Press, 2000.
Lonergan, Stephen C., and Brooks, David B. Watershed: The Role of Fresh Water in the Israeli-Palestinian Conflict. Ottawa: International Development Research Centre, 1994.
Postel, Sandra. Pillar of Sand: Can the Irrigation Miracle Last? New York: Norton, 1999.
Rogers, Peter, and Lydon, Peter, eds. Water in the Arab World: Perspectives and Prognoses. Cambridge, MA: Division of Applied Sciences, Harvard University, 1994.
Shapland, Greg. Rivers of Discord: International Water Disputes in the Middle East. New York: St. Martin's Press; London: Hurst, 1997.
Wolf, Aaron T. "Transboundary Fresh Water Database." Department of Geosciences, Oregon State University. Available from <http://www.transboundarywaters.orst.edu>.
david b. brooks
Water is the liquid of life and is crucial to every type of organism, from simple bacteria to megafauna, as well as to many of the physical processes that shape the planet, as in the weathering of mountains and valleys. For life in all forms, water is more important than even oxygen, because there exist anaerobic bacteria that can live without air but no anhydroxic bacteria that can exist without water. When astrobiologists seek to determine the possibility of life on other planets, their first question concerns the presence of water. Throughout human history, however, water has had as much a symbolic as biological significance, and human beings have adapted to environments both abundant and scarce in water, through different technological, ethical, and political engagements. Water is so rich in metaphor that it cannot be reduced to merely H2O, nor to a fluid circulated in pipes, metered, and then distributed by authorities. The duality of meaning that water embodies includes the fact that it can be both deep and shallow, life-giving and destructive, a blessing and a curse, and something that cleans the surface and also purifies the inner soul.
Water in Science
As a chemical compound water is composed of one atom of oxygen and two of hydrogen. Because acids are characterized by hydrogen ions (H+) and bases by hydroxide ions (OH−); water (H2O) may be described as neither acidic nor basic, rather equally both: The structure of water is: Oxygen is attached to two hydrogen atoms with two covalent bonds leaving two nonbonding pairs of electrons. Hydrogen bonding is particularly important in biochemical systems, because biochemical molecules contain many oxygen and nitrogen atoms that participate in hydrogen bonding. Hydrogen bonds between water molecules are responsible for the interesting physical properties of water that made it the solvent of life. Together with the extended temperature range between its solid (ice) and gaseous (steam) states, that makes liquid water able to serve as the foundation for those extremely complex carbon formations that constitute living organisms.
When present at a depth of at least two meters (six feet), pure water is a pale blue, odorless, tasteless, and transparent liquid. Other observed colors are due to various impurities, nonliving and living. It is mostly "blue water" that flows in rivers and into lakes and aquifers. "Green water" refers to the precipitation that is directly used by nonirrigated agriculture, pasture, and forests, and to evapotranspiration.
In its liquid and solid forms, water covers 71 percent of the surface area of the globe. Humanity's anthropocentric worldview explains why this mostly "blue" planet was (mis)labeled Earth. Of all the water on the planet, only 3 percent is freshwater, a figure that includes glacial ice and other hard-to-reach water sources. Of this, only 0.003 percent of the surface and subsurface water is usable by humans.
Hydrology is the science of the properties, distribution, and circulation of surface and subsurface water. In hydrologic terms, water that collects in rivers, lakes, or reservoirs is called surface water. That which seeps into the shallow or deeper layers of Earth is called aquifer. The gaseous, solid, or liquid phases of water affect both the element's chemistry such as its bonding and its physics such as its density. Water is an excellent solvent, and hence it has many constituents that are dissolved or suspended in it. These facilitate chemical interactions, which aid complex metabolisms. This explains why water is critical for all life-forms.
Pure water can be obtained through painstakingly and costly mechanical processes. Water is then the most benign of all chemical compounds known to humans. Water that contains dissolved carbonates such as calcium and magnesium is known as hard water. People notice this because it suppresses the formation of lather with soap, and when boiled, it leaves a "lime scale" that is seen in cookware. Soft water is free of such carbonates.
Water circulates from the ocean and surface of Earth to the atmosphere and then gravitates back in various forms including snow, rain, and fog. Human activities affect this hydrological cycle, most prominently through the building of physical barriers such as dams and through modifications of watersheds. Most water resources are renewable except for fossil (or connate) water that is laid down in sedimentary rocks and sealed off by overlying beds. Nevertheless, human contamination of groundwater stock, and alterations of watersheds (or, in British parlance, "drainage basins") through, for example, deforestation or paving over hydrologically critical areas can reduce aquifer recharge, alter flow characteristics, and, in severe cases, deplete a formerly renewable resource.
Many large watersheds lack time series data, and scientists in riparian states (those who study watersheds) often use different methodologies for collecting their data, which makes data sharing among water basin states ineffective and integrated management of the river system difficult.
Technologies of Water
Natural water is managed through a system of wells, dams, artificial reservoirs, conveyance systems, and human-made ponds. Humans withdraw untreated water from surface sources and pump it from aquifers. The water is treated and then pumped into carefully laid-out distribution systems such as water mains, which are connected to underground networks and sometimes to (elevated) storage facilities.
The geographical setting of the source of water, water treatment, its distribution, return flow collection, and return flow treatment—each requires a unique technological approach in order that people can access and use the resource. Economic considerations and regulations regarding human health and environmental protection also affect the choice of technology.
Easy-to-tap water sources were the first to be developed. Growing water needs require new and innovative technologies because water is increasingly extracted from deeper wells and piped in from further and further locations; furthermore, in a growing number of countries that have exhausted their supplies, freshwater is obtained by removing the salts and other contaminants from sea water (desalination). Growing water scarcity is inducing the development of water-efficient technologies. Given that agriculture is by far the largest consumer of water, drip irrigation techniques offer huge water savings, especially when compared to sprinkler irrigation or the traditional, but low-cost, flood irrigation.
Historically, the water wheel, a wheel with paddles or buckets attached to the outside, was first used to lift water from a river onto irrigation channels. Eventually, a water-powered wheel was developed and used in the Middle Ages for extracting power from a flow of water. Its applications included milling flour and machining and pounding linen for use in paper. Similarly, the steam engine contributed to Europe's economic development especially during the Industrial Revolution. This engine coverts the potential energy of the pressure in steam to mechanical work.
Water systems have been targets in warfare, and the threat of terrorism is requiring new technologies and strategies to protect water supply systems, especially in large metropolitan centers, and in countries where in which the majority of the population depends on a few desalination plants. Efforts are afoot to develop remote but real-time water-quality monitoring systems that not only encompass the traditional water-quality parameters but also can detect currently unmonitored biological agents that could threaten freshwater supplies, such as bacteria, viruses, and protozoa.
Ethics of Water
Water is central to the health of the ecosystem, central to the beliefs and customs of many religious communities, and vital to the maintenance of the economic well-being of modern and traditional lifestyles. Allocating water across competing users must thus be tempered by extensive stakeholder participation and weighed against any adverse social or ecological impacts that a solely economic approach may cause.
The increasing demand for freshwater is related to population growth, trends toward more protein-based diets, and overall improvements in the quality of life. Countries typically tap their lowest cost and most reliable sources of water first. As these sources become fully utilized, the development of new sources carries with it heavier financial costs and environmental consequences.
The equitable allocation and sustainable use of water require good governance that is rooted in policies that are scientifically, culturally, and economically sound; in institutional structures that are community friendly and invite public participation; and in decision makers who are competent and fair, and have the support of the political forces. It also requires employing modern technologies that have been adopted in many Western countries but are beyond the reach of poorer ones.
In 2002 the United Nations Committee on Economic, Social and Cultural Rights declared water a human right. It stated that the human right to water entitles everyone to sufficient, safe, acceptable, physically accessible, and affordable water for personal and domestic uses. An adequate amount of safe water is necessary to prevent death from dehydration, reduce the risk of water-related disease, and provide for consumption, cooking, and personal and domestic hygienic requirements. The signatories to the International Covenant on Economic, Social and Cultural Rights are required to progressively ensure access to clean water, equitably and without favoritism.
Politics of Water
Negotiating water-sharing agreements on for international rivers tends to be complex. Allocation agreements among competing users often involve a combination of geoclimatic factors as well as legal, historical, technological, demographic, political, and ethical considerations. In the case of international rivers, upstream states are generally seen as having leverage in influencing the allocation process simply because they control the "water tap."
Water allocation arguments include the largely discredited view that a country has an absolute sovereignty over resources that originate inside its political boundaries. Prior appropriation agreements state that the earliest users of water have rights to it. This convention is widely used in the American Southwest and by a few other countries, such as Iraq in connection with its share of the waters of the Tigris and Euphrates rivers. Before a balanced allocation formula can be reached, several factors need to be carefully considered and fairly weighted for every riparian country. These factors include a country's contribution to the total flow of the river, current and projected population size, area of arable land, and the extent to which the health of the national economy is dependent on water. A sustainable and ethical management strategy must also consider and protect the needs of aquatic life, upstream habitats (especially forests), wetlands, and floodplains, as well as the water needs of future generations. International agreements make the integrated (and sustainable) management of river systems easier.
Acute and protracted water scarcity is likely to be a source of violent conflict especially in countries where the agricultural sector is a vital contributor to national economic health. This danger has helped place water scarcity high on the world's political agenda. Globally, the overwhelming majority of water is consumed by the agricultural sector. There has been a gradual and continuing shift away from supply management to demand management of water, whereby people are asked to make the most out of their existing resources. Communities try to maximize their crop yields per unit of water (more "crop per drop") and their financial returns by planting suitable, lucrative crops. Similarly, a few arid and semiarid countries are gradually shifting away from water thirsty crops such as citrus to ones that are more suited to their own climatic and physical environments such as wheat, lentils, and chickpeas.
Immense amounts of water are wasted through leakage from antiquated urban supply networks and unsustainable irrigation strategies. Existing technologies such as the efficient, water-saving drip irrigation technique and microsprinklers have been around for decades but used on only around 1 percent of all irrigated lands. Even relatively small improvements in efficiency through the transfer of appropriate irrigation technologies and the implementation of various policy incentives and/or disincentives will result in substantial water savings.
One proposed strategy would involve governments gradually charging farmers the real and full cost of water. Progressively higher charges per unit of water consumed would induce most users to think before they turn on the water. Water quality can be protected by raising people's awareness about the adverse effects of pollution, making it prohibitively expensive to pollute, and by building sanitation infrastructures and wastewater treatment plants. This will minimize pollution levels and provide the public with recycled water to be used in nonhuman ways that do not directly affect food production, such as car washes and irrigation of lawns.
When national sources are exhausted, countries seek alternatives such as importing water, usually from nearby countries. Globalization and the opening of international markets are likely to encourage large-scale trading of freshwater across international borders. This is a controversial because of the likely environmental impacts and the political implications that a dependency on imported water may create.
Desalination, however, is an increasingly promising water-augmentation method. This process entails removing soluble salts from water to make it suitable for various human uses. Technological advances have been steadily decreasing its unit price, which is inducing more countries and facilities to use it. A growing number of countries have been increasingly adopting desalination technologies to augment their national or area-specific freshwater supplies.
HUSSEIN A. AMERY
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Faruqui, Naser I.; Asit K. Biswas; and Murad J. Bino, eds. (2001). Water Management in Islam. Ottawa: International Development and Research Centre; Tokyo: United Nations University Press. A unique anthology that outlines the potential role culture and religion could play in the protection and efficient management of water resources.
Gleick, Peter H. (2004). The World's Water, 2004–2005. Washington, DC: Island Press. A biannual report that contains impressive current data on various aspects of water resources from around the globe, and a few state of the art articles.
Illich, Ivan. (1985). H2O and the Waters of Forgetfulness. Dallas: Dallas Institute of Humanities and Culture.
Olivera, Marcela, and Jorge Vian˜a. (2003). "Winning the Water War." Human Rights Dialogue 2(9). Also available from http://www.cceia.org/viewMedia.php/prmID/951
Postel, Sandra. (1999). Pillar of Sand: Can the Irrigation Miracle Last? New York: Norton. The book examines the role irrigation played in the rise and fall of ancient civilizations. It draws on this to examine how the current growing reliance on irrigation, the mounting water scarcity, salinization of soils, and the rising tensions between riparian states affects countries and could impact them in the twenty-first century.
Stumm, Werner, and James J. Morgan. (1996). Aquatic Chemistry, 3rd edition. New York: Wiley.
Swan, C. H. (1978). "Middle East: Canals and Irrigation Problems." Quarterly Journal of Engineering Geology 11(1): 75–78.
United Nations. World Water Assessment Programme. (2003). Water for People, Water for Life. New York: UNESCO Publishing.
U.S. National Research Council, Committee on Sustainable Water Supplies for the Middle East; Israel Academy of Sciences and Humanities; Palestine Academy for Science and Technology; and Royal Scientific Society, Jordan. (1999). Water for the Future: The West Bank and Gaza Strip, Israel, and Jordan. Washington, DC: National Academy Press. Examines the need to enhance and protect sustainable water supplies in the West Bank and Gaza Strip, Israel and Jordan. It proposes criteria needed for developing sustainable water resources while maintaining environmental support systems. The collaborative study brought scientists and engineers from the U.S. National Academy of Research and from other countries in the region, and it marked unprecedented cooperation among Israel, Jordan and the Palestinian organizations.
World Commission on Dams. (2000). Dams and Development: A New Framework for Decision-Making. London: Earthscan.
If a person knows nothing else about chemistry, he or she will likely know that water is H2O. The chemical formula for water is common knowledge, used in advertisements, elementary school science classes, and casual conversation. But more than just a conversation piece, the formula H2O can tell a chemist a great deal of information.
For starters, H2O indicates that water is composed of two hydrogen atoms and one oxygen atom. That this is so can be demonstrated using very simple apparatus—a couple of pieces of wire, a battery, and some tap water. Electrolysis—the decomposition of water molecules with electricity—will result when the wires are connected to the ends of the battery and the other ends are immersed in the water with a small gap between them. One electrode releases bubbles of pure oxygen and the other pure hydrogen. Measuring the volume of gases released reveals that twice as much hydrogen is produced as oxygen. Twice as much gas means two hydrogen atoms for every one oxygen atom. Of course, this is our modern understanding of water. When these experiments were first tried, around 1800, an explanation for the results was not available. But the experiments did force scientists to think about the nature of water.
From our modern understanding of both the formula of water and the Periodic Table, we also know that the hydrogen atoms in water are bound to the oxygen. That is, water is "HOH" and not "HHO." We know that atoms can form either covalent or ionic bonds to give molecules. In water, the interaction of hydrogen and oxygen is a polar covalent bond, meaning that the two elements share a pair of electrons and that each atom contributes one of the electrons in the pair. Since hydrogen is the first element of the Periodic Table, it has only one electron and can form just one covalent bonding interaction. In the case of water, hydrogen bonds by sharing its electron with the oxygen. If hydrogen shared its electron with the other hydrogen atom in this instance, there would be no electron available to interact with the oxygen. Indeed, hydrogen gas, H2, results when two hydrogen atoms form a covalent bond, and hydrogen gas is very different from water.
In a pure (nonpolar) covalent bond, both atoms have possession of the electron pair exactly the same amount of time. In a polar covalent bond, there is unequal sharing that results from an inequity in the distribution of the electrons due to the effective nuclear charge on the atoms. This polarization of the O-H interaction is critical to explaining all of the properties of water. It results in water having a dipole with the hydrogens having a slight positive charge and the oxygen having a slight negative charge. (More precisely, the advanced explanation is that the molecular orbital that describes the oxygen-hydrogen interaction has more oxygen character, resulting in a skewed electron distribution.)
If we consider oxygen's position in the Periodic Table, we know that it starts with six valence electrons, and since it has two bonds with hydrogen, two of its electrons are involved in bonding pairs. This means that the oxygen has four electrons remaining. These electrons are organized into two "non-bonding" pairs. That is, the oxygen of water has four pairs of electrons around it—two that are interacting in polar covalent bonds with hydrogen and two that are not interacting when water is in the gaseous state. Four electron pairs means that the atoms adopt a tetrahedral arrangement with the two hydrogens occupying two corners and the electron pairs occupying the other two.
In a perfect tetrahedron, the angle between the hydrogens would be 109.5°, but because the lone pairs occupy a little more space, the experimentally measured angle in water is actually 104.5°.
The presence of two lone pairs plays a very important role in "hydrogen bonding," which is one of the most critical properties of water. The positively charged hydrogen of one water molecule can be attracted to the lone pair of an adjacent molecule, resulting in a weak hydrogen bonding interaction. This bonding is much weaker than the polar covalent bond that holds a water molecule together, but it is a substantial inter-molecular interaction resulting in two water molecules being attracted to one another. Water forms an extended network of hydrogen bonding interactions, with each water molecule capable of both creating and accepting two hydrogen bonds. As a result each and every water molecule in the liquid or solid state is surrounded by four hydrogen bonded neighbors. The presence of hydrogen bonding interactions means:
- that water has an anomalously high melting and boiling point;
- that solid water or ice is less dense than liquid; and
- that water has a high surface tension.
Melting and Boiling Point of Water
Phase changes in matter result because of a change in the translational motion of molecules. A solid is a solid because its molecules are stuck in place. In a liquid, molecules can move past one another but are still closely associated. In a gas, molecules move independent of one another and only occasionally collide. It would make sense then that lighter molecules would shift from a solid to a liquid to a gas at lower temperatures than heavy molecules because they require less energy to get moving. Consider the molecular substances in Table 1.
Hydrogen gas, being the lightest and smallest molecule in the list, has the lowest melting point ( −259°C or 14.15 K or −434°F) and boiling point ( −253°C or 20.15 K or −423°F). Similarly, of the second row compounds with hydrogen, methane (CH4) has the lowest melting and boiling points. However, water does not follow this trend. Its melting point is 0°C or 32°F. Its boiling point is 100°C or 212°F. Compared to the other molecules around it or its heavier cousin, hydrogen sulphide (H2S), water has melting and boiling points that are anomalously high. This is due to the fact that the hydrogen bonds between water molecules must be broken for a phase transition to occur. The extra energy required results in more heat being necessary and a higher temperature.
Density of Ice
Hydrogen bonding interactions between water molecules hold the molecules in place in the solid state. The O-H....O interaction spaces all of thewater molecules in an orderly array, much like students sitting in rows of desks. This spacing provides an open structure. When water is in the liquid state, the water molecules hold on to each other through hydrogen bonding interactions, but individual molecules can occupy the space between rows. The result is that at a molecular level, more liquid water molecules can occupy a given volume than when water is in the solid state. More students will fit in a classroom if they are allowed to stand than if they are arranged in nice neat rows. More molecules or more mass in a given volume means a higher density.
|PHASE CHANGES FOR SOME COMMON MOLECULAR SUBSTANCES|
|Substance||Molecular Weight (g/mol)||Melting Point ˚C||Boiling Point ˚C|
|source: Adapted from Jones, Loretta, and Atkins, Peter (1999). Chemistry: Molecules, Matter, and Change. New York: W. H. Freeman.|
The decrease in density between water and ice has a number of important implications for the world around us. Ice floats because it is less dense than liquid water. This is not true of any other liquid/solid equilibrium. Solid methane sinks in liquid methane and solid ammonia sinks in liquid ammonia. Floating ice means that ponds and lakes freeze from the top down, allowing fish and other biota to live protected from the cold weather of winter. If water froze from the bottom up, life as we know it would not have evolved on Earth.
Surface tension is a bulk property of matter and results in liquid water trying to contract to the smallest possible surface area for a given volume. Surface tension explains why water beads up on the surface of a freshly waxed car and droplets of water in a fog are spherical. The sphere is the shape with the minimum area for a given volume. Surface tension results because of the asymmetry of forces at the surface of liquid water. Water molecules at the surface are missing their hydrogen bonding interactions on one side. They are being "tugged" back into the bulk of solution.
Of course, occasionally water molecules have sufficient energy to leave the surface, resulting in evaporation. Conversely, sometimes water molecules in the gaseous state strike the surface of a drop of water and have insufficient energy to leave again. The result is condensation. The competing rates of evaporation and condensation lead to the formation of clouds and fog, to cloudy mirrors after a shower and iced-up windows on a winter's day.
Surface tension is also critical to capillary action. A surface that is covered in suitable molecules or functional groups, such as a glass surface or the cellulose of paper, will interact with water molecules and can actually draw the molecules out of the bulk. In this case, the interaction with the surface is stronger than the hydrogen bonding interaction between adjacent water molecules. As a result, water will creep up a glass tube or adsorb into paper. The latter is critically important in mopping up a spill or mess.
Water is often called the "universal solvent," as it is capable of dissolving a wide range of compounds—from sugars to salt, from DNA to hydrogen. Again, hydrogen bonding interactions play a role. For example, sugar dissolves because of the hydrogen bonding interactions between the hydroxyl groups on the sugar molecules (-OH groups) and the water molecules. But of equal importance to the dissolution of substances in water is water's capacity to act as a dipole. Water's negatively charged oxygen binds to sodium ions in salt while the positively charged hydrogens interact with the chloride ions. The result is that sodium chloride or table salt dissolves into ionic species that are more energetically stable with the sodium and chloride ions surrounded by water.
The ability of water to dissolve a wide variety of substances makes it the ideal medium for living organisms. Water's great solvency is also the reason that water pollution is so pervasive. Almost any substance will dissolve in water, including pesticides, herbicides, industrial waste, household byproducts, and a wide variety of other potentially harmful compounds. Indeed, we rely on the dissolving properties of water to get our clothes clean.
|Water Source||Water Volume(cubic miles)||Mass (kg)||Percent of Total Water|
|source: Adapted from the U.S. Geological Survey at http://ga.water.usgs.gov/edu/waterdistribution.html.|
|Icecaps, glaciers||7,000,000||2.949 1019||2.14%|
|Ground water||2,000,000||8.424 1018||0.61%|
|Fresh-water lakes||30,000||1.264 1017||0.009%|
|Saline lakes and inland seas||25,000||1.053 1017||0.008%|
|Soil moisture||16,000||6.740 1016||0.005%|
|Rivers and streams||300||1,264 1015||0.0001%|
But the dirt and grime from our clothes must end up somewhere, and that somewhere is in the water that we discharge from our homes. The Law of Conservation of Matter says that matter can be neither created nor destroyed. The atoms and molecules that we dissolve into the water in our washing machines are only being removed to another location.
Dealing with the pollution of water is a huge task, and for too long the philosophy was "the solution to pollution is dilution." Dilution is no longer an acceptable approach, as it just shifts the problem instead of addressing it. Significant effort is being spent in both addressing the real problems of water pollution and in ensuring that we have access to clean water sources. There are many techniques for purifying water, with distillation providing the cleanest and purest water. Unfortunately, distillation requires a lot of energy as it is difficult to overcome the hydrogen bonds between water molecules. Distillation also leaves behind the polluting material, which must be disposed of in a manner that does not allow it to come in contact with water and thus simply dissolve again. The difficulties of maintaining clean water is one of the major challenges facing us in the twenty-first century. For without water, life as we know it would not exist. It is because of the shape and the interactions of that very simple molecule, H2O, that water is the most essential of all chemical compounds.
see also Green Chemistry; Molecular Geometry; Valence Bond Theory; Water Pollution; Water Quality.
Todd W. Whitcombe
Atkins, Peter W. (1987). Molecules. New York: Scientific American Library.
Leopold, Luna B.; Davis, Kenneth S.; and the Editors of Life (1966). Water. New York: Time Incorporated New York.
Stanitski, Conrad L.; Eubanks, Lucy Pryde; Middlecamp, Catherine H.; and Pienta, Norbert J. (2003). Chemistry in Context : Applying Chemistry to Society. New York: McGraw-Hill.
Water is a chemical compound (H2O) composed of a single oxygen (O) atom bonded to two hydrogen (H) atoms, which are separated by an angle of 105°. Because of this asymmetrical arrangement, water molecules have a tendency to orient themselves in an electric field, with the positively charged hydrogen toward the negative pole and the negatively charged oxygen toward the positive pole. This tendency results in water having a large dielectric constant, which is responsible for making water an excellent solvent. Water is, therefore, commonly referred to as the universal solvent. Water is the most abundant liquid on Earth. It covers more than 70% of Earth’s surface. Including the clouds (which are, of course, also water), it makes the entire planet look blue and white from space. About 97.5% of Earth’s water is contained in seawater. Approximately 1.875% is found in polar ice caps. The remaining 0.625% is drinkable water.
Since mineral salts and organic materials can dissolve in water, it is the ideal medium for transporting life-sustaining minerals and nutrients into and through animal and plant bodies. Brackish and ocean waters may contain large quantities of sodium chloride (NaCl) as well as many other soluble compounds leached from the crust of Earth. For example, the concentration of mineral salts in ocean water is about 35,000 parts per million. Water is considered to be drinkable if it contains less than 500 parts per million of salts. Water can be reused indefinitely as a solvent because it undergoes almost no modification in the process.
Hydrogen bonding, which joins water molecule to water molecule, is responsible for other properties that make water a unique substance. These properties include its large heat capacity, which causes water to act as a moderator of temperature fluctuations; its high surface tension (due to cohesion among water molecules); and its adherence to other substances, such as the walls of a vessel (due to adhesion between water molecules and the molecules of a second substance). The high surface tension makes it possible for surface-gliding insects and broad, flat objects to be supported on the surface of water. Adhesion of water molecules to soil particles is the primary mechanism by which water moves through unsaturated soils.
Water is the only common substance that occurs naturally on Earth in three different physical states. The solid state, ice, is characterized by a rigid crystalline structure occurring at or below 32° F(0° C) and occupying a definite volume (found as glaciers and ice caps, as snow, hail, and frost, and as clouds formed of ice crystals). The liquid state exists over a definite temperature range 32 to 212° F (0° C to 100° C), but is not rigid nor does it have a particular shape. In other words, it has a definite volume but assumes the shape of its container. Liquid water covers three-fourths of Earth’s surface in the form of swamps, lakes, rivers, and oceans as well as found as rain clouds, dew, and ground water. The gaseous state forms at temperatures above 212° F(100° C), and neither occupies a definite volume nor is rigid. In other words, it takes on the exact shape and volume of its container. It occurs naturally as fog, steam, and clouds. One phase does not suddenly replace its predecessor as the temperature changes, but for a time at the melting point or boiling point, two phases will coexist. As water changes from the gaseous form to the liquid form, it gives off heat at about 540 calories per gram, and as it changes from the liquid form to the solid form, it gives off about 80 calories per gram. The turbulence of thunderstorms is in large part due to the release of large amounts of energy into the atmosphere as water condenses into water droplets or into crystals of ice (i.e., hail). Pressure affects the transition temperature between phases. For example, at pressures below atmospheric pressure, water boils at temperatures under 212° F(100° C), so food will take longer to cook at higher elevations.
Water can pass directly from the solid phase to the gaseous phase without going through the liquid phase. This process occurs at low temperatures and greatly reduced pressures through a process called sublimation. Dehydrated foods are produced by sublimation, in which foods are quick-frozen and then placed in evacuation chambers. Dehydration by sublimation requires less energy than other methods, reduces physical deterioration that accompanies prolonged or excessive heating, and decreases the loss of volatile aromatic compounds responsible for flavor.
Earth’s supply of water is constantly being recycled. It is evaporated from the oceans by the sun and is given off by the forests. The vapor condenses into clouds, which rain out onto the land. The land water runs off into the lakes and rivers, which then run back to the seas, and the cycle is complete. The total amount of water on Earth, in the form of oceans, lakes, rivers, clouds, polar ice, etc., is 1.5× 1018(one-and-a-half billion) tons, occupying a total volume of 8.7 million cubic miles.
It is impossible to overstate the importance of water to almost every process on Earth, from the life processes of the lowest bacteria to the shaping of continents. Water is the most familiar of all chemical compounds known to humans. It is essential to all living things, plant and animal. Humans drink it, wash with it, play in it, and cook in it. In fact, human bodies are more than one-half water.
Scientists never see absolutely pure water because it dissolves so many substances. If people want pure water, then scientists have to prepare it laboriously by such means as distillation, ion exchange, and reverse osmosis. Moving water even dissolves rock slightly, to form caves and to wear away mountains. All of the water on Earth, therefore, is in the form of solutions. The dissolved substances change the properties of water from what they would be in pure water. They affect its freezing point and its boiling point, among many other physical and chemical properties. The dissolved or suspended substances in water can be in the form of ions, molecules, or larger particles. For drinking water, bacteria must also be killed.
Water is an odorless, tasteless, transparent liquid that appears colorless but is actually very pale blue. The color is obvious in large quantities of water such as lakes and oceans, but it can even be seen in a full bathtub. It is a single chemical compound whose molecules consist of two hydrogen atoms attached to one oxygen atom. The chemical formula of this compound is therefore H2O. The two hydrogen atoms are attached to the oxygen atom in such a way as to make an angle-shaped molecule. The angle is not 90°, however, but 104.5°—close to a right angle, but a little wider.
The formula H2O means that no matter how much water is talked about, it always contains exactly twice as many hydrogen atoms as oxygen atoms. Considering that a hydrogen atom weighs only about one-sixteenth as much as an oxygen atom, most of the weight in water is due to oxygen: 88.8% of the weight is oxygen and 11.2% is hydrogen. That goes for everything from a single molecule to a lake.
Water can be made (synthesized) from hydrogen and oxygen, both of which are gases. When these two gases are mixed, however, they do not react unless the reaction is started with a flame or spark. Then, they react with explosive violence. The tremendous energy that is released is a signal that hydrogen and oxygen are very eager to become water. Another way of saying that is that water is an extremely stable compound, compared with loose molecules of hydrogen and oxygen. It is hard to break water molecules apart into its components.
Not only that, but water molecules are stuck quite tightly to each other—at least when compared with similar compounds. The molecule-to-molecule stickiness is caused mainly by the fact that the water molecule is a dipole, because the oxygen atom pulls electrons away from the hydrogen atoms, giving the oxygen corner of the molecule a slight negative charge and the two hydrogen ends a slight positive charge. The negative part of one water molecule then attracts the positive parts of others like a magnet, although they can still slide around over each other as molecules do in any liquid. Water molecules stick to each other also by hydrogen bonds.
The strong attractions that water molecules have for each other are responsible for many of water’s highly unusual properties, as compared with other liquids of about the same molecular weight. Among these are:
- Its unusually high boiling point (if it were similar to the other liquids, it would be a gas at room temperature).
- Its high heat of vaporization (the amount of heat it takes to change the liquid to a gas).
- Its high heat of fusion (the amount of heat it takes to melt solid ice).
- Its high heat capacity (the amount of heat it takes to raise its temperature by a certain amount).
- Its world-champion rank among liquids as a solvent (it has been called the universal solvent because it dissolves so many different substances).
- The low density (the lightness) of ice, which makes it float on the surface of liquid water. As water is cooled to make ice, it gets slightly denser, like all liquids. But at 39.2° F(4° C) it reaches its maximum density; when cooled below that temperature, it gets less dense until it reaches 32° F (0° C), at which time it freezes and suddenly decreases to 91.7% of the density of the water. Being less dense than the water, the ice floats.
The normal boiling point of water is 212° F (100° C), and its freezing point is 32° F (0° C). In fact, zero and 100 degrees on the Celsius scale are defined as the freezing and boiling points of water. Water is also the standard by which many other quantities are measured. For example, the density of a material is often expressed as its specific gravity or specific weight: how many times denser it is than water.
In pure water, one out of every 555 million molecules is broken down—dissociated—into a hydrogen ion and a hydroxide ion:
These ions are enough to make water a slight conductor of electricity. That is why water is dangerous when there is electricity around. The slight dissociation of water is responsible for the acid and base balances of all of the chemical reactions that take place in water, and that includes almost all the chemical reactions that take place anywhere, including those in the human body. Acid-base balance is probably the most important single factor that affects chemical reactions.
Water is a major geologic agent of change for modifying Earth’s surface through erosion by water and ice. Water is also an important recreational medium, supporting fishing, swimming, and boating, and is a major factor in the tourism industry.
Water is scarce in many parts of the world, while it is plentiful in others. Many water resource experts state that water will become the next major commodity traded internationally. It has been called such phrases as liquid gold and the oil of the twenty-first century because of the increasing demands made by humans on water.
Editors of I.B. Tauris. A History of Water. London, UK, and New York: I.B. Tauris, 2004.
Hancock P.L., and Skinner B.J., eds. The Oxford Companion to the Earth. Oxford: Oxford University Press, 2000.
Herschy, Reginald, and Rhodes Fairbridge, eds. Encyclopedia of Hydrology and Water Resources. Boston: Kluwer Academic Publishing, 1998.
Lide, D.R., ed. CRC Handbook of Chemistry and Physics Boca Raton: CRC Press, 2001.
McConnell, Robert, and Daniel Abel. Environmental Issues: Measuring, Analyzing, Evaluating. 2nd ed. Englewood Cliffs, NJ: Prentice Hall, 2002.
Oxtoby, David W., et al. The Principles of Modern Chemistry. 5th ed. Pacific Grove, CA: Brooks/Cole, 2002.
Robert L. Wolke
Water is a chemical compound needed by most plants and animals on Earth in order to sustain life. Pure water is a tasteless, odorless, transparent liquid. In small amounts it is colorless, but it takes on a bluish tint in larger amounts. Water is an excellent solvent and as a result it usually contains a wide variety of dissolved minerals and other chemicals. It can also carry and support bacteria. Most of the water distributed through municipal water systems is treated to remove harmful substances. Some bottled waters undergo even further treatment to remove almost all impurities. The English word water is derived from the German word wasser, which in turn is derived from an ancient Indo-European word meaning to wet or wash.
The controlled use of water dates to at least 8,000 b.c. when farmers in Egypt and parts of Asia trapped floodwaters for crop irrigation. The concept of using irrigation canals to bring water to crops, rather than waiting for a flood, was first developed about 2,000 b.c. in Egypt and Peru. By about 1,000 b.c., the city of Karcho, in what is now Jordan, built two aqueducts to bring an adequate supply of water for the city's population. This is the first recorded instance of a planned municipal water supply.
Early water treatment was surprisingly advanced, although rarely practiced. An ancient Sanskrit manuscript, from what is now India, advises that drinking water should be kept in copper vessels, exposed to sunlight, and filtered through charcoal. Ancient Egyptian inscriptions give similar advice. Many of these methods are still used today. In about 400 b.c., the Greek medical practitioner Hippocrates suggested that water should be boiled and strained through a piece of cloth. Despite these early references, most people drank untreated water from flowing streams or subterranean wells. As long as there were no sources of contamination nearby, this was a satisfactory solution.
As the population of Europe and other parts of the civilized world grew, their sources of water became increasingly contaminated. In many cities, the rivers that served as the primary sources of drinking water were so badly contaminated with sewage that they resembled open cesspools. Cholera, typhoid, and many other water-borne diseases took their toll. In 1800, William Cruikshank of England demonstrated that small doses of chlorine would kill germs in water. By the 1890s, several municipalities found that slowly filtering water through beds of sand could also significantly reduce the incidence of disease. The public outcry for safe drinking water reached such a crescendo that by the early 1900s most major cities in the United States had installed some sort of water treatment system.
Even with water treatment, water contamination remained a serious concern as an increasing amount of industrial wastes poured into the nation's rivers and lakes. As the adverse health effects of lead, arsenic, pesticides, and other chemicals became known, the United States federal government was obliged to pass the Water Pollution Control Act of 1948. This was the first comprehensive legislation to define and regulate water quality. It was followed by a series of increasingly tougher requirements, culminating in the current Environmental Protection Agency (EPA) water quality standards. In addition to the federal standards, most states have their own water quality laws, and some state laws are more stringent than those specified by the EPA.
Types of Water
Pure water is an almost non-existent entity. Most water contains varying amounts of dissolved minerals and salts, plus an abundance of suspended particles such as silt and microscopic organic material. Different types of water are classified by the presence or absence of these impurities.
Tap water, or municipal water, has under-gone a series of treatments to kill harmful bacteria, remove sediments, and eliminate objectionable odors. It may also have had one or more chemicals added for a variety of reasons.
Hard water contains high amounts of calcium and magnesium salts. This causes soap to form curds. Hard water is further divided into temporarily hard water and permanently hard water. Temporarily hard water contains bicarbonates of calcium and/or magnesium, which react to form a hard substance called scale when the water is heated. Scale can clog hot water heaters and pipes and leave deposits on cooking utensils. Permanently hard water contains sulphates, chlorides, or nitrates of calcium and/or magnesium, which are not affected by heating. Soft water contains relatively low amounts of calcium and magnesium salts, although the definition of "low" varies. The term "softened water" refers to hard water that has had enough salts chemically removed to avoid forming soap curds. It is high in sodium chloride.
If water contains a large quantity of dissolved minerals, it is called mineral water. Mineral waters can be divided into five main classes: saline, alkaline, ferrunginous, sulphurous, and potable. Saline water has a high level of sodium or magnesium sulphate or sodium chloride. Alkaline water has a high concentration of salts which give it a pH in the range of about 7.2-9.5, where a pH of 7 is neutral and a pH of 14 is highly alkaline. Ferrungious water is rich in iron, which gives it a rusty color. Sulphurous water is rich in sulphur compounds and is distinguished by its rotten egg smell. Potable water has a mineral content of less than 500 parts per million and is most commonly bottled and sold as a specialty drinking water.
Carbonated water, soda water, and sparkling water all contain dissolved carbon dioxide. This may occur naturally where limestone or other carbonate rocks are present, or the carbon dioxide may be added artificially under pressure.
Spring water and artesian water are distinguished only by the fact that they flow from the ground naturally without the aid of drilling or pumping. Otherwise, there is nothing that makes them different than water from other sources.
Distilled water has been purified by an evaporation-condensation process that removes most, but not all, impurities. Deionized water has been purified by an ion-exchange process, which removes both positive ions, such as calcium and sodium, and negative ions, such as chlorides and bicarbonates. It is sometimes called de-mineralized water. Purified water is municipal water that has undergone carbon filtration, distillation, deionization, reverse osmosis, ultraviolet sterilization, or some combination of these processes to remove almost all minerals and chemical elements, both good and bad.
A water molecule consists of two atoms of hydrogen bonded to one atom of oxygen. The chemical symbol is H2O. Water usually also contains a wide range of organic and inorganic materials in solution or suspension.
In the process of treating water for use in a municipal system, several chemicals may be added. These include disinfectants like chlorine, chloramine, or ozone; coagulantants like aluminum sulfate, ferric chloride, and various organic polymers; acidity neutralizers like caustic soda or lime; and chemicals to help prevent tooth decay in the form of various fluoride compounds.
The Treatment Process
The specific water treatment process depends on the intended application. Some water, such the water used to irrigate crops, receives no treatment. Other water, such as the water used to make pharmaceuticals, is highly purified.
Here is a typical series of operations used to treat municipal water for distribution to homes and businesses.
- 1 Most municipal water comes from two sources: ground water and surface water. Most ground water is tapped by drilling wells into the underground water-bearing layer called the aquifer. Some ground water rises naturally in the form of springs. Surface water is tapped by impounding rivers behind dams. The surrounding area that drains into the rivers is called the watershed. In many cases, access to and use of the watershed is limited to prevent contamination of the runoff water.
- 2 From the well or dam, the water is carried to the water treatment plant in open canals or closed pipes. In some cases, the water supply is close to the municipality. In other cases, the water has to be transported many hundreds of miles (km) to reach its destination. Sometimes the water is stored in intermediate reservoirs along the way to ensure that there will always be an adequate supply available to meet a city's fluctuating needs.
- 3 In some water treatment plants, the water is initially disinfected by contact with ozone-rich air in a series of chambers. This step is used by most plants in Europe, but only a few plants in the United States. Ozone (03) is formed by passing compressed air through a high-voltage electric arc. This causes some of the oxygen (02) molecules in the air to split in half and reattach themselves to other oxygen molecules to form ozone. Ozone effectively kills most germs and also destroys compounds, which cause unpleasant tastes and odors. It has a relatively short life, however, and does not remain in the water to protect it during storage and distribution. For this reason, a small dose of chlorine or chloramine is added to the water at the end of the treatment process.
- 4 The water then passes through a flash mixer where chemicals known as coagulants are rapidly mixed with the water. The coagulants alter the electric charge around any suspended particles in the water and make them attract each other and clump together, or coagulate.
- 5 The water moves slowly through a series of chambers where it is gently mixed by the swirling flow. As the water mixes, the charged particles continue to bump into each other and form even larger particles called flocs.
- 6 The water flows into a settling basin or tank where the heavy flocs sink to the bottom. Some settling basins have two levels to double their capacity. The material that settles to the bottom is vacuumed out of the basin with a device like a pool vacuum and is deposited in a solids holding basin. The trapped material from the filter (step 7) is also added to the solids holding basin. These combined materials are sent through a gravity thickener and then a press where most of the water is squeezed out. The remaining solids are loaded into trucks and transported to a landfill for disposal.
- 7 The partially cleaned water passes through several layers of sand and pulverized coal, which trap any very small particles that remain in the water. Some harmful organisms are also trapped this way in those water treatment plants that do not use ozone as an initial disinfectant. The filter layers are back-flushed periodically to remove the trapped material.
- 8 In some plants, the water is passed through a bed of activated charcoal granules. Chemical contaminants in the water stick to the surface of the charcoal in a process known as carbon adsorption.
- 9 In some areas where the water contains undesirable amounts of iron and manganese or certain dissolved gases, the water is sprayed into the air from large basins to aerate it. When the water mixes with the air, it picks up oxygen, which causes some of the contaminants to settle out. Other contaminants are removed by evaporation.
- 10 In some water treatment plants, a fluoes ride compound is added to the water to help prevent tooth decay. Fluoride occurs naturally in some water supplies and additional amounts are not required. In the past, fluoridation has been a hotly debated subject, and not every municipality adds fluoride to their water.
- 11 Other chemicals may be added to the water to help reduce corrosion in pipes and plumbing fixtures. This is done by adding controlled amounts of certain chemicals to adjust the pH factor to a neutral level.
- 12 As the water leaves the treatment plant, it receives a small dose of chlorine or chloramine to kill any harmful bacteria that may have found their way into the distribution system. If the plant does not use ozone as an initial disinfectant, a larger amount of chlorine or chloramine is added to the water.
- 13 After the water leaves the plant, it is usually stored in covered tanks or reservoirs to protect it from contamination. In some areas, these storage facilities are located at a higher elevation than the surrounding terrain, and the water is pumped up into the tank or reservoir. This elevated storage position provides the pressure necessary for adequate flow through the water mains and pipes within the city. In other cases, the water is stored in ground-level facilities, and the pressure is supplied by electric pumps that run on demand.
The federal and state water quality standards set maximum contamination levels for more than 90 organic, inorganic, microbiological, and radioactive materials that may be found in water. These standards are further divided into primary standards, which cover materials that may be harmful to humans, and secondary standards, which cover materials and properties that may affect aesthetic qualities such as taste, odor, and appearance. A typical water district may perform more than 50,000 chemical and bacteriological analyses of the water supply each year to ensure the standards are being met.
The public's concern over safe drinking water is expected to result in even more stringent water quality standards in the future. Ironically, one of the most recent concerns is not about outside contamination, but about the effects of one of the substances commonly used to disinfect water—chlorine. Studies within the last 30 years have shown that chlorine forms certain compounds with the organic materials found in water. The most common compounds are called trihalomethanes, or THMs, which have a 1-in-10,000 risk of causing cancer when ingested or inhaled over a long period. One alternative to using chlorine is chloramine, which is a combination of ammonia and chlorine that does not form THMs as readily. Many water treatment plants have already switched to chloramine. Other alternative disinfectants include ozone, ultraviolet light, chlorine dioxide, and a hybrid of ozone and hydrogen peroxide called peroxone.
Where to Learn More
von Wiesenberger, Arthur. H2O: The Guide to Quality Bottled Water. Woodbridge Press, 1988.
Water Quality Standards Handbook, 2nd edition. United States Environmental Protection Agency, 1994.
Arrandale, T. "A Guide to Clean Water." Governing (December 1995): 57-60.
Wasik, J. F. "How Safe is Your Water?" Consumers Digest (May/June 1996): 63-69.
"Alameda County Water District Water Treatment Facility." Pamphlet. Alameda County Water District, 1993.
"Layperson's Guide to Drinking Water." Pamphlet. Water Education Foundation, 1995.
wa·ter / ˈwôtər; ˈwä-/ • n. 1. a colorless, transparent, odorless, tasteless liquid that forms the seas, lakes, rivers, and rain and is the basis of the fluids of living organisms. ∎ this as supplied to houses or commercial establishments through pipes and taps: each bedroom has a washbasin with hot and cold water | [as adj.] water pipes. ∎ one of the four elements in ancient and medieval philosophy and in astrology (considered essential to the nature of the signs Cancer, Scorpio, and Pisces): [as adj.] a water sign. ∎ (usu. the waters) the water of a mineral spring, typically as used medicinally for bathing in or drinking: resorts where southerners came to take the waters. ∎ a solution of a specified substance in water: ammonia water. ∎ urine: drinking alcohol will make you need to pass water more often. ∎ (waters) the amniotic fluid surrounding a fetus in the womb, esp. as discharged in a flow shortly before birth: I think my waters have broken.2. (the water) a stretch or area of water, such as a river, sea, or lake: the lawns ran down to the water's edge. ∎ the surface of such an area of water: she ducked under the water. ∎ [as adj.] found in, on, or near such areas of water: a water plant. ∎ (waters) the water of a particular sea, river, or lake: the waters of Hudson Bay | fig. the government is taking us into unknown waters with these changes in the legislation. ∎ (waters) an area of sea regarded as under the jurisdiction of a particular country: Japanese coastal waters.3. the quality of transparency and brilliance shown by a diamond or other gem.4. Finance capital stock that represents a book value greater than the true assets of a company.• v. 1. [tr.] pour or sprinkle water over (a plant or an area of ground), typically in order to encourage plant growth: I went out to water the geraniums. ∎ give a drink of water to (an animal): they stopped to water the horses and to refresh themselves. ∎ [intr.] (of an animal) drink water. ∎ (usu. be watered) (of a river) flow through (an area of land): the valley is watered by the Pines River. ∎ take a fresh supply of water on board (a ship or steam train): the ship was watered and fresh livestock taken aboard. ∎ Finance increase (a company's debt, or nominal capital) by the issue of new shares without a corresponding addition to assets.2. [intr.] (of the eyes) become full of moisture or tears: Rory blinked, his eyes watering. ∎ (of the mouth) produce saliva, typically in response to the sight or smell of appetizing food: the smell of frying bacon made Hilary's mouth water.3. [tr.] dilute or adulterate (a drink, typically an alcoholic one) with water: staff at the club had been watering down the drinks. ∎ (water something down) make a statement or proposal less forceful or controversial by changing or leaving out certain details: the army's report of its investigation was considerably watered down.PHRASES: by water using a ship or boat for travel or transport: at the end of the lake was a small gazebo, accessible only by water.cast one's bread upon the waterssee bread.like water in great quantities: George was spending money like water.make water1. urinate.2. (of a ship or boat) take in water through a leak.of the first water (of a diamond or pearl) of the greatest brilliance and transparency. ∎ (typically of someone or something perceived as undesirable or annoying) extreme or unsurpassed of their kind: she was a bore of the first water.under water submerged; flooded.the water of life whiskey.water off a duck's backsee duck1 .water on the brain inf. hydrocephalus.water under the bridge (or water over the dam) used to refer to events or situations that are in the past and consequently no longer to be regarded as important or as a source of concern.DERIVATIVES: wa·ter·er n.wa·ter·less adj.ORIGIN: Old English wæter (noun), wæterian (verb), of Germanic origin; related to Dutch water, German Wasser, from an Indo-European root shared by Russian voda (compare with vodka), also by Latin unda ‘wave’ and Greek hudōr ‘water.’
Water is hydrogen oxide and it is composed of two molecules of hydrogen and one molecule of oxygen. It has a molecular weight of 18.016 and is the most universal solvent known.
Water is the most universal solvent known. In the human body, it is capable of dissolving simple elements, ions and large organic molecules. Because of water's ability to maintain these materials in solution, the various body chemicals are capable of undergoing reactions that would not be possible in other forms.
Because water is a liquid, it can be carried through the circulatory system, reaching to all cells in the body.
Water is the most common compound in the human body, although the percentage of body water will vary from individual to individual, depending on age, gender, and general body composition. Newborn infants are about 78% body water, but this drops to
Daily adequate intake of water
|Age||Approximate daily intake of water (cups)*|
|Children 0—6 mos.||3|
|Children 7—12 mos.||3 1/3|
|Children 1—3 yrs.||5K2|
|Children 4—8 yrs.||7|
|Boys 9—13 yrs.||10|
|Girls 9—13 yrs.||8-9|
|Boys 14—18 yrs.||14|
|Girls 14—18 yrs.||9-10|
|Women 19> yrs.||11½|
*Includes water contained in food, beverages, and drinking water
SOURCE: Adapted from the Dietary Reference Intakes Table, Food and Nutrition Board, Institute of Medicine, National Academies
(Illustration by GGS Information Services/Thomson Gale.)
65% by one year of age. Although the adult percentages are often quoted as 60% for males and 55% for females, this is strongly influenced by the amount of body fat present in the body. Since fat cells contain very little water, higher levels of body fat will reduce the overall percentage of water.
Intracellular fluid, the liquid inside individual cells, represents about two-thirds of the body's water. or about 40% of total body weight. Intracellular fluid contains both water and salts, primarily potassium, as well as enzymes and other organic molecules. Flow of water into and out of the cell is largely controlled by osmosis. The outermost layer of an animal cell is the cell membrane, and water can flow through the membrane from areas of low salt concentration to areas of high salt concentration. The remaining water is in the form of extracellular fluid that includes blood and cerebrospinal fluid. The most common ion of the extracellular fluid is sodium. Body water may be lost through various mechanisms including respiration, perspiration, and urination, and must constantly be replaced. Under the best circumstances, water levels will be completely balanced, and the intake will match the amount of water lost.
Because water can be moved through the body rapidly, people have used diuretics to give the illusion of weight loss. Diuretcis, both drugs and diuretic herbs, promote loss of water through the kidneys. Water loss is at best transient, and has no real benefit in terms of either health or physical appearance.
Dehydration —A condition of water loss caused by either inadequate intake of water or excessive loss of water as through vomiting or diarrhea.
Hyperhydration —Excess water content of the body.
Hyponatremia —Inadequate sodium levels in the body, possibly caused by loss of sodium through perspiration, diarrhea, or vomiting, and replacement of fluids with water that does not contain adequate electrolytes.
Molecular weight —The total of the atomic weights of the atoms in a molecule.
Pre-loading —Administering in advance, such as drinking water prior to exercise that is likely to cause water loss.
Water intoxication —A condition caused by excessive water in the body, related to hyponatremia.
Beyond its role in general health, water can make play a major role in maintaining body weight through a program of caloric restriction. Foods that contain large amounts of water, such as fruits and vegetables, have low energy density, and so may produce sensations of satiety with low caloric intake.
Several published studies showed interesting patterns of food intake based on the water composition of foods. In one, subjects were given either food containing a high concentration of water, such as a soup of a stew, or the same solids prepared as a casserole, with water to accompany the meal. Although in each case, the total amount of both solids and water were the same, subjects ingested fewer calories when the water was incorporated into the food source. In a related study, advising people to eat foods with low energy density, that is, foods containing higher concentrations of water, was a more successful weight-loss strategy than attempts to limit portion size.
The second study evaluated the effects of preloading water before a meal. Subjects were asked to drink water before eating. Although subjects claimed that the quantity of water ingested had filled them up, and they had no appetite, the amount of food actually consumed after the pre-load was no different from that eaten by members of the control group. Although these studies are not definitive, they do indiate that foods with a high concentration of water, such as soups, stews, or salads, may be useful in weight loss programs by providing satiety with low levels of energy intake.
Failure to maintain adequate water levels can lead to dehydration. While this may be the result of various diseases, the initial symptoms are thirst and dry mouth. followed by lightheadedness and dizziness
Although water intake is normally very safe, excessive water intake, also known as hyperhydration, can occur, and may be fatal. Excessive water intake can lead to dilution of the sodium levels in the body, causing hyponatremia. This condition is sometimes seen in infants who may ingest too much water, either because they are given only water to drink or because excessive water is used to dilute infant formulas. Water intoxication may also result from severe vomiting or diarrhea in which the fluid is replaced with water, without replacing the electrolytes. Rarely, athletes who have undergone very great extertion may perspire excessively, and, if the fluid loss is replaced with water without electrolytes, may experience water intoxication. Althoug this is very rare, it did occur at the 2007 London Marathon, when temperatures were unseasonably warm that over 5,000 runners needed to be treated on site. Over 70 runners were taken to the hospital for treatment and one first-time marathoner, 22 years of age, died from hyperhydration. Voluntary hyperhydration has been reported and has been known to be fatal. On occasion, hyperhydration has been reported as part of school hazings.
Symptoms of water intoxication are similar to those of dehydration: muscle cramps, confusion, nausea, slurred speech and disorientation. Because of this, althletes may mistake water intoxication for dehydration, and drink even more water after toxicity has appeared. The goal of rehydration is to drink just enough water to replace the amount lost to perspiration. Forcing fluids can be dangerous. While sports drinks replace electrolytes, they may also provide a high level of calories. For people exercising to lose weight, an appropriate amount of water has been advocated as the most appropriate method of rehydration.
Weight loss programs should target body fat; however, some weight-loss remedies, in an attempt to show prompt results, have incorporated diuretic drugs. These may lead to loss of body water, with the risk of dehydration.
Adolescents and teen-agers should be aware of the hazards associated with hyperhydration. Children of this age may be at risk both of excessive water intake after athletics, and also as part of school hazing rituals.
Lide, David, editor. CRC Handbook of Chemistry and Physics, 87th edition. Boca Raton, Florida: CRDC Press, 2006.
Gray RW, French SJ, Robinson TM, Yeomans MR.
“Increasing preload volume with water reduces rated appetite but not food intake in healthy men even with minimum delay between preload and test meal.” Nutr Neurosci. 2003 Feb; 6(1): 29-37.
Keating JP, Schears GJ, Dodge PR. Oral water intoxication in infants. An American epidemic. Am J Dis Child.1991 Sep; 145(9): 985-90.
Norton GN, Anderson AS, Hetherington MM. “Volume and variety: relative effects on food intake.” Physiol Behav. 2006 Apr 15; 87(4): 714-22. Epub 2006 Mar 3.
Rolls BJ,Bell EA,Thorwart ML. “Water incorporated into a food but not served with a food decreases energy intake in lean women.” Am J Clin Nutr. 1999 Oct; 70(4): 448-55.
Stiefel D, Petzold A. “H2O Coma.” Neurocrit Care. 2007; 6(1): 67-71
Baby Milk Action. 34 Trumpington Street, Cambridge, CB2
1QY UK. Phone: 01223 464420; +44 1223 464420 (outside UK). <http://www.babymilkaction.org>
Urgent Care Association of America. 4320 Winfield Road, Suite 200 Warrenville, IL 60555. Phone: (877) 698-2262. <http://www.ucaoa.org.>
Samuel D. Uretsky, PharmD
Solar System, Water in the
Solar System, Water in the
Liquid water is an essential ingredient for all life on Earth. With 70 percent of its planetary surface covered by water, Earth is unique in the solar system. Earth is the only planet known to have indigenous life; yet water, mostly as water ice, is found throughout the solar system.
Why is water so abundant on Earth? The answer lies in the materials from which the planets were formed, the conditions under which the planets formed, and the properties of water. Hydrogen and lesser amounts of helium were the most abundant ingredients of the "chemical stew" from which the solar system emerged. Oxygen, one of the most common products of nuclear fusion, is found throughout the molecular clouds from which new stars and new solar systems are born. Oxygen combines with hydrogen to make H2O, or water.
The Inner Terrestrial Planetary Bodies
In the solar system, inward of the asteroid belt , oxygen combined with elements such as silicon, aluminum, and calcium to make minerals and rocks that formed the inner terrestrial planetary bodies (Mercury, Venus, Earth, the Moon, and Mars). Beyond the asteroid belt, in the colder conditions of the outer solar system, water condensed to form ice grains that were incorporated in the giant planets (Jupiter, Saturn, Uranus, and Neptune) and their moons.
Mercury, the closest planet to the Sun with an average distance to the Sun of 0.387 astronomical unit , or about 58 million kilometers, is in a very unusual elliptical orbit around the Sun. It spins three times around its own rotational axis for every two times that it orbits the Sun. This results in the greatest range of temperature extremes in the solar system. Daytime surface temperatures on Mercury can rise to 800 kelvin, then fall to 90 kelvin during the night. In other words, temperatures can range from about 525°C (980°F) down to −180°C (−297°F).
Although Mercury is one of the Earth's closest neighbors in the solar system, it has been studied very little and the majority of detailed information on the closest planet to the Sun was gathered during three Mariner flyby missions during 1974 and 1975. Mercury's closeness to the Sun makes it particularly difficult to observe with conventional telescopes, but advances in radar techniques in the 1990s revealed large deposits of possible water ice (equivalent to thousands of cubic kilometers) in permanently shaded craters near the poles of Mercury.
The cloud layers that permanently shroud Venus are largely composed of carbon dioxide and sulfur gases, but include water vapor. In a runaway greenhouse effect , the clouds reflect the thermal energy radiated from the surface of Venus back onto the surface, resulting in the high surface temperatures of around 450°C (842°F). However, this may not always have been the case. Studies of the decomposition of hydrous minerals (minerals that contain water) at extreme temperatures provide tentative indirect evidence that Venus may have had surface water in the past. The hot and dry Venus of today may have been a wet planet in the past, like Earth and ancient Mars.
Water that was present during the formation of Earth and the other planets was incorporated into the bedrock of the planets or on their surfaces. Much of the water on Earth today may have been delivered by cometary and asteroidal bombardment several hundred million years after the planet formed. That includes the water in the atmosphere, the oceans, the polar caps and glaciers, in human bodies, and in all other living things in the biosphere.
The existence of water ice in polar regions of the Moon was first suggested in the late 1800s. The Lunar Prospector mission, launched in January 1998, carried an instrument that detected possible indications for water ice at both the north and south poles of the Moon. While some scientists contemplated deep frozen reservoirs in permanently shaded craters, the widespread nature of the signals suggest the water may be bound up in clays. The possible presence of water on the Moon—in any form—would be a great natural resource for future human missions (for propulsion as well as drinking water) and would provide valuable information about earlier conditions in the Earth–Moon system.
Water is certainly present on Mars. There is water vapor in the Martian atmosphere that forms into white clouds, fog, and frost. Water ice exists in a residual polar cap at its north pole. Images provided by the Mars Global Surveyor spacecraft suggested the existence of subsurface water on Mars, and the Mars Odyssey spacecraft confirmed the presence of significant amounts of subsurface water on Mars via gamma-ray spectrometer measurements of subsurface hydrogen. These measurements indicate the presence of a considerable amount of water a few meters below the Mars surface. Further discussions of water on Mars may be found elsewhere in this encyclopedia.
Asteroids and Comets
Many planetary scientists believe that cometary impacts early in Earth's history could have supplied much of the water for its oceans. Further discussions of asteroidal and cometary water may be found elsewhere in this encyclopedia.
The Outer Solar System
The outer solar system is locked in a permanent ice age. Even so, water is present in the atmospheres of Jupiter, Saturn, Uranus, Neptune, and Pluto. Uranus and Neptune contain much larger proportions of ice-forming and rock-forming constituents than Jupiter or Saturn. Density and gravity field data for Uranus and Neptune, together with theories of the formation of those gas giants, suggest that both have massive global oceans of water ice.
Water condenses in the atmosphere of Jupiter. When the Galileo spacecraft arrived at Jupiter in 1995, it released a probe that measured levels of atmospheric water significantly lower than the expected abundance; however, the probe unexpectedly descended through a very dry part of the Jovian atmosphere.
Satellites of the Outer Solar System Planets.
The low bulk density of most of the outer solar system satellites (moons) indicates that they are composed from 30 percent to 70 percent of ice, mixed with higher density rock. The ice component includes water ice, carbon dioxide ice, carbon monoxide ice, and nitrogen ice.
Spectroscopic observations and magnetic field measurements taken by the Galileo spacecraft found evidence for the presence of liquid water under the frozen surfaces of three of Jupiter's four Galilean satellites: Callisto, Europa, and Ganymede. In the case of Ganymede, the water appears to be between 145 and 193 kilometers (90 and 120 miles) below the surface. Ganymede, the largest satellite in the solar system, is larger than either Mercury or Pluto.
Water ice has also been detected on all of the major satellites of Saturn and Uranus. The exterior layers of Pluto and Triton are composed of nitrogen, carbon monoxide, carbon dioxide, and water ices.
see also Astrobiology: Water and the Potential for Extraterrestrial Life;Comets and Meteorites, Water in; Earth: The Water Planet; Earth's Interior, Water in the; Mars, Water on; Volcanoes and Water.
Cattermole, Peter. Venus. Baltimore, MD: Johns Hopkins University Press, 1994.
Dasch, Pat, ed. Space Sciences. New York: Macmillan Reference USA, 2002.
Spudis, Paul D. The Once and Future Moon. Washington, D.C. and London, U.K.:Smithsonian Institution Press, 1996.
TYPES OF ICE
The term "water ice" may seem redundant to most people, because frozen water is commonly encountered on Earth. Yet within the solar system, gases such as carbon dioxide, carbon monoxide, and nitrogen can exist as ice on the surface of planetary bodies. Hence, the descriptor "water ice" is necessary to distinguish it from carbon dioxide ice or other icy forms.
Water is an odorless, tasteless, transparent liquid that appears colorless but is actually very pale blue. The color is obvious in large quantities of water such as lakes and oceans. Water is the most abundant liquid on Earth. In its liquid and solid (ice) form, it covers more than 70 percent of Earth's surface—an area called the hydrosphere.
Earth's supply of water is constantly being replaced through a natural cycle called the hydrologic cycle. Water is continually evaporating from the surface of the planet, condensing in the atmosphere, and falling back to the surface as precipitation.
It is impossible to overstate the importance of water to almost every process on Earth, from the life processes of the lowest bacteria to the shaping of continents. Water is the most familiar of all chemical compounds known to humans. In fact, the human body is composed mainly of water.
Chemical properties of water
Water is a single chemical compound whose molecules consist of two hydrogen atoms attached to one oxygen atom. The chemical formula of this compound is H2O. Considering that a hydrogen atom weighs only about one-sixteenth as much as an oxygen atom, most of the weight in water is due to oxygen: 88.8 percent of the weight is oxygen and 11.2 percent is hydrogen. This percentage remains the same from a single water molecule to a lake full of water molecules.
Water can be made (synthesized) from hydrogen and oxygen, both of which are gases. When these two gases are mixed, however, they do not react unless the reaction is started with a flame or spark. Then they react with explosive violence. The tremendous energy that is released is a signal that water is an extremely stable compound. It is hard to break a water molecule apart into its components.
The normal boiling point of water is 212°F (100°C) and its freezing point is 32°F (0°C). As water is cooled to make ice, it becomes slightly denser, like all liquids. But at 39.2°F (4°C), it reaches its maximum density. When cooled below that temperature, it becomes less dense. At 32°F (0°C), water freezes and expands. Since ice is less dense than water, ice floats on it.
In pure water, 1 out of every 555 million molecules is broken down into a hydrogen ion and a hydroxide ion (an ion is an electrically charged atom or group of atoms). These ions are enough to make water a slight conductor of electricity. That is why water is dangerous when there is electricity around.
Because water dissolves so many substances (it is called the universal solvent), all of the water on Earth is in the form of solutions.
Words to Know
Aquifer: Underground layer of sand, gravel, or spongy rock that collects water.
Estuary: Lower end of a river where ocean tides meet the river's current.
Hydrologic cycle: Continual movement of water from the atmosphere to Earth's surface through precipitation and back to the atmosphere through evaporation and transpiration.
Ion: A molecule or atom that has lost one or more electrons and is, therefore, electrically charged.
The oceans contain more than 97 percent of all the water on Earth. However, seawater is unsuitable for drinking because of the large amount of dissolved salts in it. The six most abundant elements making up these salts in seawater are chlorine, sodium, sulfur, magnesium, calcium, and potassium. Chlorine and sodium, the most abundant of these elements, combine to form sodium chloride, more commonly known as table salt.
These elements are deposited in seawater through various means. Volcanic activity (on land and on the seafloor) releases chlorine and sulfur. Other elements reach the oceans through runoffs from land. Rain and other precipitation weathers and erodes rocks and soil on land, dissolving the minerals (salts) they contain. This material is then transported to the oceans by rivers.
Salinity is the measure of the amount of dissolved salts in seawater. This measurement is usually the mass of material dissolved in 1,000 grams (35 ounces) of water. The average salinity of seawater is about 35 grams (1.2 ounces) of salts in 1,000 grams (35 ounces) of seawater, or 3.5 percent of the total.
Hard water is water that contains large amounts of ions (electrically charged particles) of calcium, magnesium, or iron. Hard water often has an unpleasant taste, interferes with the ability of soaps to dissolve, and can cause scaling (the building up of insoluble material) in pipes and hot water systems.
Water hardness is most commonly the result of acidic water containing carbon dioxide passing through limestone or dolomite and dissolving the minerals these rocks contain. The dissolved minerals lead to an increase in the amounts of calcium and magnesium ions in the water.
Hard water can be treated by boiling the water, but this method is effective only for small quantities. A more efficient method is to use ion-exchangers, in which the unwanted calcium and magnesium ions are exchanged or traded for sodium ions that do not cause scaling. Most water softeners work by the ion-exchange method. The soft water that is produced is not free of ions, only of undesirable ions.
Desalination. Desalination is the process of removing salt from sea-water to provide essential water for drinking, irrigation, and industry, especially in desert regions or areas where freshwater is scarce. In the almost 4,000 desalination plants worldwide, most desalination takes place through two methods: distillation and reverse osmosis.
At its simplest, distillation consists of boiling seawater to separate it from dissolved salt. Once the seawater boils, water vapor rises, leaving the salt on the bottom of the tank. The water vapor is then transferred to a separate, cooler tank where it condenses as pure liquid water. Heat for distillation usually comes from burning fossil fuels (oil and coal). Distillation is widely used in the Middle East, where fossil fuel is plentiful but freshwater is scarce.
Reverse osmosis uses high pressure to force pure water out of saltwater. Pressures up to 60 atmospheres (800 to 1,200 pounds per square inch) are applied to saltwater, forcing it through a special membrane that allows only pure water to flow through, trapping the salt on the other side. Reverse osmosis is widely used to desalinate brackish water, which is less salty than seawater and therefore requires pressures only about one-half as great.
Brackish water has a salinity between that of freshwater and seawater. Brackish waters develop through the mixing of saltwater and freshwater. This occurs mostly near the coasts of the oceans in coastal estuaries (the lower course of a river where it flows into an ocean) or salt marshes that are frequently flooded with ocean currents due to the rising and falling of tides.
Most species can tolerate either saltwater or freshwater, but not both. Organisms that live in brackish habitats must be tolerant of a wide range of salt concentrations. The small fish known as killifish are common residents of estuaries, where within any day the salt concentration in tidal pools and creeks can vary from that of freshwater to that of the open ocean. During their spawning migrations, salmon and eels experience a range of salt concentration as they move through all three water environments: seawater, brackish water, and freshwater.
Freshwater is chemically defined as water that contains less than 0.2 percent dissolved salts. Of all the water on Earth, less than 3 percent is freshwater. About two-thirds of all freshwater is locked up in ice, mainly in Greenland and the Antarctic.
The remaining freshwater—less than 1 percent of all the water on Earth—supports most plants and animals that live on land. This freshwater occurs on the surface in lakes, ponds, rivers, and streams and underground in the pores in soil and in subterranean aquifers in deep geological formations. Freshwater also is found in the atmosphere as clouds and precipitation.
Worldwide, agricultural irrigation uses about 80 percent of all freshwater. The remaining 20 percent is used for domestic consumption, as cooling water for electrical power plants, and for other industrial purposes. This figure varies widely from place to place. For example, China uses 87 percent of its available water for agriculture. The United States uses 40 percent for agriculture, 40 percent for electrical cooling, 10 percent for domestic consumption, and 10 percent for industrial purposes.
[See also Hydrologic cycle; Lake; Ocean; River ]