WATER

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

SEE ALSO Acid Mine Drainage;Air;Dams;Deforestation and Desertification;Earth;Environmental Ethics;Fire.

BIBLIOGRAPHY

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