What Is Water?
What Is Water?
Most people living in the United States assume they will have plenty of clean, safe water for drinking, that crops and gardens can be regularly irrigated, and that sewage will be taken care of by their local treatment plant. In many parts of the world, however, the availability of water for personal and public use cannot be taken for granted. In fact, according to the World Health Organization (WHO), in "Water, Sanitation, and Hygiene Links to Health: Facts and Figures" (November 2004, http://www.who.int/water_sanitation_health/factsfigures2005.pdf), 17% of the population around the world—1.1 billion people—did not have access to safe water in 2002.
Water is vital to human survival. Although people can survive for a month—possibly two—without food, they would die in about a week without water. Water is the most common substance on Earth. It covers three-fourths of the earth's surface and makes up about 65% of the adult human body, including 90% of its blood and 75% of its brain. Water is the main ingredient in most of the fruits, vegetables, and meats that people eat. According to the fact sheet "Safe Drinking Water Act 30th Anniversary: Water Facts" (June 2004, http://www.epa.gov/ogwdw/sdwa/30th/factsheets/waterfacts.html) by the U.S. Environmental Protection Agency, water makes up about 75% of a chicken, 80% of a pineapple, and 95% of a tomato. In Water—More Nutrition per Drop (2004, http://www.siwi.org/downloads/More_Nutrition_Per_Drop.pdf), the Stockholm International Water Institute and the International Water Management Institute report that growing enough food to produce an adequate diet for a human being for one year requires 1,300 meters cubed (343,421 gallons) per person per year, or about 941 gallons of water per person per day.
Even though it is essential to human existence, water can cause severe damage and destruction. It is terror to the swimmer caught up in a current. It contributes to rusting in cars and rotting in wood. Water in the form of hailstones can destroy crops, and in the winter ice coats roads making driving dangerous. Too much rain can cause flooding, which has the potential for destroying homes and killing people. Too little rain can result in droughts, which have the potential to cause living things to dehydrate and eventually die. Water can carry pathogens, which cause disease; in developing countries waterborne diseases are commonplace.
WATER'S CHEMICAL COMPOSITION
Water is a molecule comprised of two hydrogen (H) atoms and one oxygen (O) atom. (See Figure 1.1.) The atoms in a molecule of water share electrons, forming strong chemical bonds that hold water molecules together. Water is also both a weak acid and a weak base—chemical properties that allow it to dissolve many substances.
THREE STATES OF WATER
Water exists naturally in three states: a liquid (its most common form), a solid (ice), and a gas (water vapor). It is the only substance on Earth in which all three of its natural states occur within the normal range of climatic conditions, sometimes at the same time. Familiar examples of water in its three natural states are rain, snow or hail, and steam.
Compared with other liquids, water has some unusual properties. For example, most liquids contract (shrink) as they freeze. That is, their molecules move closer together. Water contracts only until it reaches 4° Celsius (C) or 39.2° Fahrenheit (F). Then it expands (its molecules move farther apart from one another) until it reaches its freezing point of 0°C (32°F). This expansion can exert a tremendous force on surrounding objects, enough to crack an unprotected automobile engine, burst a basement water pipe, or even shatter a boulder. Expansion makes ice less dense than water, which is why ice floats. This phenomenon causes ice to form on rivers and lakes from the top down, and aquatic life survives beneath the ice.
When ice is warmed to a temperature higher than 0°C, it melts, becoming liquid. As a liquid, its molecules are more loosely bound together than in the "locked" crystalline lattice of ice, and they can move around each other rather freely. The molecules' ability to slip and slide around gives water and other liquids their fluid properties.
In the gaseous or vapor state, water molecules move rapidly about and have little attraction for each other, creating the diffuse appearance of steam or mist, or the haze of a humid day. (Humidity is the measure of the amount of water vapor in the air.) Evaporation is the general term used to describe the process by which water in its liquid form is changed to its gaseous state. Evaporation can occur under a wide variety of conditions. Examples include water vaporizing off of wet pavement following rainfall, boiling in a pot on the stove and producing steam, or evaporating from clothes hanging on a line to dry.
WATER: THE EARTH MOVER
Scientists believe the earth formed about four billion years ago. Within its primitive atmosphere were the basic elements needed to form water. As the earth cooled from a mass of molten rock, water formed in the atmosphere and then fell to the ground in a rain that lasted for many years, forming the oceans.
The flow of water flattens mountains and cuts canyons deep into the surface of the earth. It hollows out underground caverns and leaves behind attractive formations. Water creates soil by breaking down rocks and organic material and depositing it elsewhere. Water in the form of ice redesigned the face of the earth as glaciers advanced and receded many thousands of years ago. The slow, relentless processes of water freezing, melting, flowing, and evaporating will likely make the earth's appearance as different a million years from today as it was a million years ago.
The U.S. Geological Survey (USGS) notes in Where Is Earth's Water Located? (August 28, 2006, http://ga.water.usgs.gov/edu/earthwherewater.html) that the earth is a vast reservoir, containing an estimated 332.5 million cubic miles of water (a cubic mile of water equals 1.1 trillion gallons). It is all around us: in the atmosphere, on the earth's surface, and in the ground. The relative distribution of the world's water supply is shown in Figure 1.2. About 97% of water on Earth is saltwater in the oceans, and about 3% is freshwater. Of the freshwater, 68.7% comprises ice caps and glaciers, 30.1% is groundwater (water found within the ground), and 0.3% is surface water (water at the surface, such as lakes and rivers). Only 0.9% of water is found in the atmosphere, mainly in the form of invisible water vapor.
Of all this water, what can humans use for their daily water needs? The 97% of water found in the oceans cannot be used unless the salt is removed. The desalination process is quite costly, although recent technologies have made this process economically more attractive. Any community, business, or industry that considers desalination as a method of obtaining freshwater must determine whether the cost of desalination is lower than the cost of other water supply alternatives. Most of the desalination facilities currently in operation around the world are in the Middle East. The article "Largest Desalination Plant Opens in Ashkelon" (Israel High-Tech and Investment Report, September 2005) explains that in August 2005 Israel began operation of the world's largest desalination plant. Located along the country's southern Mediterranean coast, it provides a hundred million cubic meters of desalinated water per year, about 15% of the total household water in Israel. In the United States, Florida and California have desalination plants. The California Coastal Commission indicates in Seawater Desalination and the California Coastal Act (March 2004, http://www.coastal.ca.gov/energy/14a-3-2004-desalination.pdf) that California's 11 plants provide about 3 million gallons per day and that the state plans on building 21 more facilities, which will provide about 240 million gallons per day.
Most of the water people use everyday, however, comes from rivers, which is only 2% of all surface water, and surface water makes up only 0.3% of all the water on Earth. (See Figure 1.2.) Most of the freshwater available for use (30.1% of all freshwater) is stored in the ground. The rest of the freshwater on Earth is not available for human use because it is frozen in icecaps and glaciers.
As shown in Figure 1.3, the earth's water is continually being cycled between the ground and the air. This exchange is caused by the heat of the sun and the force of gravity. Water evaporates from the surface of the earth (e.g., from moist ground, the leaves of vegetation, and bodies of water). It then rises into the atmosphere as water vapor. The water vapor condenses to a liquid from its gaseous form and falls as precipitation, in the form of rain, mist, sleet, hail, or snow.
The precipitation, in turn, replenishes the earth's surface and underground waters, which eventually join the ponds, lakes, rivers, and oceans. Evaporation of water from the land and oceans and transpiration from plants (evaporation of water from the leaves), which together are called evapotranspiration, put the water (as vapor) back into the air. In this way water travels from the ground to the atmosphere and back to the ground continuously. The exchange of water between the ground and the air is called the hydrologic cycle or water cycle. (See Figure 1.3.) The term hydrologic is derived from two Greek words: hydro, which means water, and loge, an ancient Greek word meaning "knowledge of."
The hydrologic cycle is a natural, constantly running distillation and pumping system. As a cycle, this flow has no beginning and no end. Within the hydrologic cycle water is neither lost nor gained; it simply changes form as it moves through the cycle. The molecules of water in the world's oceans, lakes, rivers, ponds, streams, and atmosphere today are the same molecules that formed four billion years ago.
Although constantly in motion, water is transferred between phases of the hydrologic cycle at different rates, depending on where it is located. For instance, a water molecule exists as water vapor in the atmosphere an average of eight days, but when it enters the ocean it may remain there for the next twenty-five hundred years.
The hydrologic cycle shapes and sustains life on Earth. It is largely responsible for determining climate and types of vegetation. Because it is an open system, outside actions may affect any phase of the cycle, and they may have both immediate and long-term consequences.
Although it represents only a small percentage of Earth's water supply, soil moisture is extremely significant. It supplies water to plants, a vital link in the food chain. Some plants grow directly in water or in marshy ground, but most live on dry land. This is possible because the land is truly dry in just a few places, and often only temporarily.
Dust is generally considered dry, but the dust kicked up by a car on a dry dirt road may contain up to 15% water by weight. Vegetation, however, cannot grow and flourish on that road because soil holds its small percentage of moisture so strongly that plant roots cannot get it out. Other than desert plants, which store water in their own tissues during infrequent wet periods, most plants can grow only where there is extractable water in the soil. Because the earth's vegetation continually withdraws moisture from the ground in large amounts, frequent renewals of soil moisture, either by precipitation or irrigation, are needed.
Rain, snow, sleet, and hail are all forms of precipitation. This moisture in the air comes from the evaporation of water from the ground and from bodies of water such as lakes, rivers, and, especially, the oceans. Plants also release moisture into the air through their leaves. This process is called transpiration. The plant moisture is first taken up by the roots from the soil, moves up the plant in the sap, and then emerges from the plant through thousands of tiny holes on the underside of each leaf. According to the USGS, in "The Water Cycle: Evapotranspiration" (August 25, 2005, http://ga.water.usgs.gov/edu/watercycleevapotranspiration.html), an acre of corn transpires three to four thousand gallons of water every day and a large tree may release over one hundred gallons per day.
Transpiration from plants is one of the important sources of water vapor in the air and usually produces more moisture than evaporation from the ground, lakes, and streams. The most important source of water vapor in the air, however, is evaporation from the oceans, especially those parts of the ocean that are located in the warmest parts of the planet. Heat is required to change water from a liquid to a vapor. Thus, the higher the temperature, the faster the water evaporates from the oceans. However, the winds in the upper atmosphere carry this moisture far from the oceans. Someone who lives in the central part of the United States, for example, may receive rain that is composed of water particles evaporated from the ocean near the equator or the Gulf of Mexico.
Ice Caps and Glaciers
About two-thirds of all freshwater in the world is stored as ice. (See Figure 1.2.) According to the article "Antarctic Ice Sheet Losing Mass, Says University of Colorado Study" (ScienceDaily, March 2, 2006), most of the world's ice is held by the Antarctic ice cap—about 90% of all existing ice. However, this ice sheet has lost significant mass in recent years due to changing climate conditions.
Ice is also held in glaciers. A glacier is any large mass of snow or ice that persists on land for many years and moves under its own weight. Glaciers are formed in locations where, over a number of years, more snow falls than melts. As this snow accumulates, it compresses and changes into dense, solid ice—a glacier.
Robert M. Krimmel notes in Glaciers of the Coterminous United States (March 7, 2002, http://pubs.usgs.gov/pp/p1386j/us/westus-lores.pdf) that even though most people associate glaciers with remote, frozen regions such as Antarctica, there are more than sixteen hundred glaciers in the lower forty-eight U.S. states, most of them quite small. They cover about 227 square miles in parts of California, Colorado, Idaho, Montana, Nevada, Oregon, Utah, Washington, and Wyoming. Alaska has uncounted numbers of glaciers that cover many thousands of square miles.
Permafrost is permanently frozen ground, which comprises approximately one-fifth of Earth's entire land surface. It exists in Antarctica but is more extensive in the Northern Hemisphere. In the land surrounding the Arctic Ocean, its maximum thickness has been measured in thousands of feet—about 5,000 feet (1,524 meters) in Siberia and 2,000 feet (610 meters) in Alaska. Even though the surface permafrost (called the active layer, see Figure 1.4) thaws quickly in the summer and refreezes in winter, it would take thousands of years of thawing conditions to melt the thick, frozen layer beneath. The deepest part of permafrost was formed during the Great Ice Age, which occurred about three million years ago. Talik, which is shown in Figure 1.4, are patches of ground within permafrost that never freeze because of a local irregularity in conditions.
In North America the discovery of gold in Alaska and the Yukon in the early 1900s sparked an increased interest in the nature of the vast areas of permafrost. After World War II (1939–45), increasing numbers of nonnative people migrated to areas of frozen ground, and the construction of roads, railroads, and buildings and the clearing of land led to the disruption and thawing of previously undisturbed permafrost. This caused unstable ground, landslides, mudflows, and, consequently, dangerous living conditions. In addition, Larry C. Smith et al. report in "Disappearing Arctic Lakes" (Science, June 3, 2005) that warming in the Arctic, which has sped up since the 1980s, is causing the loss of permafrost in Arctic regions.
Except for the disruption of day-to-day life caused by winter snowstorms in certain areas of the United States, most Americans are largely unaware of the importance of snow. Unlike many other countries, the United States is economically dependent on snow. Almost all the water in the arid West that can be tapped on a large-volume basis comes directly from spring snowmelt. The amount of water in a given year's snowpack varies greatly from one year to another. The snowpack volume is of crucial importance to regional economics. Too much snow can cause flooding and extensive damage to crops, livestock, businesses, and homes. Too little can mean shortages in water for drinking, irrigation, and hydroelectric power, affecting their availability and cost.
The importance of snow is highlighted by Mark H. Hunter in "San Luis Valley Still in the Grip of Record Drought. Snowpack Goes into Ground, Not Streams" (Denver Post, May 2, 2003). Hunter describes drought conditions in northern Colorado, caused in part by a significant decrease in snowpack in the upper Rio Grande basin. According to Hunter, in 2003 snowpack in the upper Rio Grande basin was only 71% of average, with a snowwater content of thirteen inches. Drought conditions had affected the region for three consecutive years, diminishing the San Luis Valley's underground aquifer. The aquifer sustains thousands of acres of natural wetlands and half a million acres of farm and ranch land. The area's snowpack improved somewhat in 2004 and 2005, but the effects of the drought are still being felt.
Despite the enormous amount of water that surrounds us, only about 3% of it is freshwater and, therefore, suitable for use by land-based animals, plants, and humans. (See Figure 1.2.) The availability of freshwater depends on many factors: climate, location, rainfall, and local activity. The USGS reports in Where Is Earth's Water Located? that the world's freshwater lakes contain 21,830 cubic miles of water, and the world's rivers contain 509 cubic miles of freshwater. Together, lakes and rivers make up about 0.0072% of the total water on Earth. Groundwater (subsurface water) totals about 5.6 million cubic miles or 1.7% of the total water supply.
VARIATIONS IN PRECIPITATION
The amount of precipitation that falls around the world can range from less than one-tenth of one inch per year in the deserts to hundreds of inches per year in the tropics. In "Global Measured Extremes of Temperature and Precipitation" (August 9, 2004, http://www.ncdc.noaa.gov/oa/climate/globalextremes.html#highpre), the National Climatic Data Center reports that the lowest average annual precipitation occurs in Arica, Chile, with 0.03 inches. The world's wettest spot is Lloro, Colombia, with an average annual rainfall of 523.6 inches.
Variations in precipitation occur not only in various regions of the globe but also seasonally and annually. For example, southern Florida has a rainy season (May to October) followed by a dry season (November to April). Most of the forty-five to sixty inches of annual rain that falls (under normal conditions) in this area occurs in the rainy season. In exceptionally dry years, droughts occur because the area receives little or no precipitation in the rainy season; in exceptionally wet years, flooding may occur.
Natural phenomena known as El Niño and La Niña influence weather and precipitation. El Niño is a naturally occurring disruption of the ocean-atmosphere system in the tropical Pacific Ocean, which has important consequences for weather around the globe. It is characterized by an unusually warm current of water that appears every three to five years in the eastern Pacific Ocean. Unusually warm sea surface temperature results in a decline in primary productivity (microscopic plants and animals) that in turn brings sharp declines in commercial fisheries and bird populations that are also dependent on fish. Unusual weather conditions occur around the globe as jet streams, storm tracks, and monsoons are shifted. Some other consequences are increased rainfall across the southern United States and Peru that has caused destructive flooding in the past, and drought in Australia and Indonesia. El Niño brings warmer than normal temperatures to the north-central states and cooler than normal temperatures to the southeastern and southwestern United States.
La Niña global climate impacts tend to be the opposite of El Niño because La Niña is characterized by unusually cold ocean temperatures in the equatorial Pacific. In the United States winter temperatures are warmer than normal in the Southeast and cooler than normal in the Northwest. La Niña events occur after some, but not all, El Niño events. Generally, La Niña occurs half as frequently as El Niño.
HUMAN INFLUENCES ON WATER
As populations continually modify the environment to suit their needs and desires, the natural processes, including the hydrologic cycle, are significantly disrupted. People are finding out that the earth, even with its remarkable recuperative powers, has limits beyond which it cannot sustain a livable environment.
There are two ways by which humanity can change the basic quality and natural distribution of water: by introducing materials and organisms into a body of water (including the atmosphere)—commonly known as pollution—and by intervening in any phase of the hydrologic cycle in such a way that the cycle is altered. Dams, irrigation, and hydroelectric plants are examples of alterations.
For centuries, the world's lakes, rivers, and oceans have been dumping sites for many of the undesirable byproducts of civilization. People have dumped indiscriminately, believing that bodies of water had an inexhaustible capacity to disperse and neutralize any amount of waste. What was not dissolved or dispersed settled to the bottom, where it could not be seen.
Dumping waste into the oceans and waterways led to few apparent problems as long as waste products were few and consisted mainly of naturally occurring materials. However, as the world's population grew and technology began introducing huge numbers of new products and processes, this natural disposal system began breaking down under an overload of natural and synthetic contaminants. Fish and marine animals died; dead zones, where no life could survive, developed in harbors and oceans; drinking water became contaminated; and beaches became littered with garbage.
|Sources of water pollution|
|Source: "Table 1-1. Pollution Source Categories Used in This Report," in National Water Quality Inventory: 1998 Report to Congress, U.S. Environmental Protection Agency, Office of Water, June 2000, http://www.epa.gov/305b/98report/chap1.pdf (accessed January 4, 2007)|
|Industrial||Pulp and paper mills, chemical manufacturers, steel plants, metal process and product manufacturers, textile manufacturers, food processing plants|
|Municipal||Publicly owned sewage treatment plants that may receive indirect discharges from industrial facilities or businesses|
|Combined sewer overflows||Single facilities that treat both storm water and sanitary sewage, which may become overloaded during storm events and discharge untreated wastes into surface waters|
|Storm sewers/urban runoff||Runoff from impervious surfaces including streets, parking lots, buildings, and other paved areas|
|Agricultural||Crop production, pastures, rangeland, feedlots, animal operations|
|Silvicultural||Forest management, tree harvesting, logging road construction|
|Construction||Land development, road construction|
|Resource extraction||Mining, petroleum drilling, runoff from mine tailing sites|
|Land disposal||Leachate or discharge from septic tanks, landfills, and hazardous waste sites|
|Hydrologic modification||Channelization, dredging, dam construction, flow regulation|
|Habitat modification||Removal of riparian vegetation, streambank modification, drainage/filling of wetlands|
Water that has been physically or chemically changed and that adversely affects the health of humans and other organisms is said to be polluted. There are many sources and types of water pollution. Every day, industrial byproducts and household wastes such as toxic chemicals, metals, plastics, medical refuse, radioactive waste, and sludge (the solid material left after water is extracted from raw sewage) are deposited into the nation's rivers, lakes, harbors, and oceans. Septic tanks, landfills, and mining operations often produce hazardous substances that seep into the soil and then into underground aquifers (areas within subsurface rock where water is stored). Table 1.1 lists the most common sources of water pollution. (The term riparian, which is used in Table 1.1, refers to the banks of a body of water, such as a riverbank.) Figure 1.5 shows how bacteria, viruses, and other pathogens can be introduced into water.
Water pollution is acknowledged by both scientists and the WHO as a global problem and one that results in the serious health issue of waterborne disease. Concern over water pollution helped launch the environmental movement of the 1970s. The 1972 Federal Water Pollution Control Act, commonly known as the Clean Water Act, was the first major piece of environmental legislation enacted by Congress. Since then, many laws and regulations designed to protect, preserve, and clean up the national waters have been passed. Although substantial progress has been made, many problems remain to be solved.
Point and Nonpoint Sources of Pollution
There are two types of water pollution sources: point and nonpoint sources. Point sources are specific sites, such as sewage treatment plants, factories, and ships, which discharge pollutants into bodies of water at single points via pipes, sewers, or ditches. Nonpoint sources are not specific sites; pollutants enter bodies of water over large areas rather than at single points. Nonpoint sources of water pollution include agricultural runoff, mining activities, and soil erosion.
The Water Pollution Control Act and its amendments, such as the Clean Water Act, established the National Pollutant Discharge Elimination System, which controls water pollution by regulating point sources. This system uses water quality standards and discharge permits as a means of regulation. Water quality standards establish the upper limit for the amount of a pollutant that will not cause an adverse effect on humans or other species. Cities, companies, and other entities that want to discharge into water apply for permission and if approved receive a permit. The permit specifies the amount and type of pollutants that may be discharged and not cause a violation of the water quality standard. Dischargers are required to monitor what they release and report the results. When limits are exceeded, fines and other penalties are imposed, including requirements for additional treatment and cleanup.
Nonpoint sources of pollution are harder to control. Agriculture results in a great deal of nonpoint source pollution. For example, when water runs off fertilized land, it carries fertilizer with it into bodies of water. Fertilizer promotes the growth of plants and algae in the water. A high concentration of plant and algal growth results in the water becoming cloudy with their growth and, therefore, light cannot easily penetrate. When the reduced levels of light and the concentration of nutrients can no longer support high plant and algal growth, these organisms die, fall to the bottom, and decay. As bacteria feed on the dead plant material, they use oxygen, which results in less dissolved oxygen for fish. Fish that need higher levels of oxygen die out, whereas other species that can survive in low oxygen levels multiply. The dead fish decay as well—a process that lowers the dissolved oxygen even more. At this point, the water is said to be eutrophic and may become slimy and smelly.
Human Activities That Contribute to Water Pollution and Degrade Water Quality
Many human activities promote water pollution. For example, modern technological developments allow massive quantities of water to be pumped out of the ground for use as drinking water and irrigation of crops. When large amounts of water are removed from the ground (and from the water cycle), underground aquifers can become depleted much more quickly than they can naturally replenish themselves. In some areas this has led to the subsidence, or sinking, of the ground above major aquifers. Removing too much water from an aquifer in coastal areas can result in saltwater intrusion into the aquifer, rendering the water too brackish (salty) to drink. The natural filtering process that occurs as water travels through rocks and sand is also impaired when aquifer levels become depleted, leaving the aquifer more vulnerable to contamination.
Building dams also interferes with the hydrologic cycle and may promote water pollution. The huge dams built in the United States just before and after World War II have substantially changed the natural flow of rivers. By reducing the amount of water available downstream and slowing stream flow, a dam not only affects a river but also the river's entire ecological system. For example, wetlands have the ability to clean water by trapping and filtering pollutants. This water-cleansing process can be stopped or reduced if dams cause wetlands to dry up.
Deforestation and overgrazing worldwide have destroyed thousands of acres of vegetation that play a vital role in controlling erosion. Erosion is the process by which a material is worn away by a stream of water or air, usually because of the abrasive particles in the water or air. Erosion results in soil runoff into rivers and streams, causing turbidity (cloudiness or discoloration), siltation (depositing of soil on the bottoms of rivers and streams), and disruption of stream flow. Removal of vegetation on the land also reduces the amount of water released into the atmosphere by transpiration. In some areas less water in the atmosphere can mean less rainfall, causing fertile regions to become deserts.
Along with agricultural activities, industrial, urban, and residential development can also lead to soil runoff. As Figure 1.6 shows, timber harvesting leads to compacted soil, less ground cover, and disturbed ground. Some agricultural and industrial practices also lead to these results, along with fewer riparian areas. Building roads results in compacted soil and fewer floodplains and wetlands. Urbanization (the building of cities with paved surfaces covering the land) leads to all these results. Under these conditions storms often lead to increased turbidity, flooding, runoff, and erosion.
WORLDWIDE WATER CRISIS
Despite conservation (the careful use and protection of water resources) and reclamation (the treatment of wastewater so that it can be reused) efforts to lessen the effects of human activities on water quality, the world still faces a severe scarcity of sanitary water. According to Dan Vergano, in "Water Shortages Could Leave World in Dire Straits" (USA Today, January 26, 2003), the United Nations (UN) predicts that within fifty years more than half of the world's population will be living with water shortages, depleted fisheries, and polluted coastlines. Based on data provided by the National Aeronautics and Space Administration, the WHO, and other organizations, the UN notes that the severe water shortages faced by at least four hundred million people in 2003 will affect four billion people by 2050. The UN also concludes that waste and inadequate management of water, especially in poverty-stricken areas, are the main causes of the problems.
The scarcity of clean water throughout the world also has significant implications for public health. The UN Educational, Scientific, and Cultural Organization (2006, http://www.unesco.org/water/wwap/facts_figures/basic_needs.shtml) finds that water contaminated with bacteria, parasites, and other microbes causes about 6,000 deaths every day, including 1.3 million children under the age of five.
Water shortages also affect international politics. In Global Water Futures (2005, http://www.sandia.gov/water/docs/Global_Water_Futures.pdf), the Center for Strategic and International Studies estimates that more than 260 of the world's river basins are shared by at least two countries. Conflicts arise when one country tries to dam up, siphon off, or pollute the shared water. According to Meredith A. Giordano and Aaron T. Wolf, in Atlas of International Freshwater Agreements (November 2003, http://www.transboundarywaters.orst.edu/publications/atlas/), since 1820 there have been more than four hundred agreements related to water as a limited and consumable resource. They note that while cooperation about water resources between and among countries during the past fifty years has outnumbered conflicts by more than two to one, problems still occur. For example, between 1948 and 2002 Giordano and Wolf count thirty-seven incidents of violent conflict over water, thirty of which were between Israel and one or another of its neighbors. Peter H. Gleick, in "Water Conflict Chronology" (October 12, 2006, http://worldwater.org/conflictchronology.pdf), identifies several more instances between 2003 and 2006, including disputes in Colombia, Ethiopia, India, Iraq, Israel, Kenya, Lebanon, Mexico, Pakistan, Somalia, Sri Lanka, Sudan, and Yemen.