WORLDWIDE SUPPLY Water covers 71% of Earth’s surface. Earth’s organisms are made up mostly of water. Only a tiny faction of the planet’s abundant water is available to us as fresh water. About 97% is found in the oceans. The remaining 3% is fresh water. About 2.997% is locked up in ice caps or glaciers, or is buried so deep that it costs too much to extract. SURFACE WATER The fresh water we use comes from two sources: surface water and groundwater. Precipitation that does not soak into the ground or return to the atmosphere by evaporation or transpiration is called surface water. Watersheds, also called drainage basins, are areas of land that drain into bodies of surface water. Water flowing off the land into these bodies is called surface runoff. GROUNDWATER Some precipitation infiltrates the ground and fills the pores in soil and rock. The sub-surface area where all available soil and rock spaces are filled by water is called the zone of saturation, and the water in these pores is called groundwater. The water table is the upper surface of the zone of saturation. The ability of soil or rock to hold water depends on its porosity and permeability. Porous, water-saturated layers of sand, gravel, or bed rock through which groundwater flows and that can yield an economically significant amount of water are called aquifers. Most aquifers are replenished naturally by precipitation, which percolates downward in what is called natural recharge. Any area of land through which water passes into an aquifer is called a recharge area. Groundwater moves from the recharge area through an aquifer and out to a discharge area (well, spring, lake, geyser, stream, or ocean) as part of the hydrologic cycle. There is 40 times more groundwater than surface water. If you withdraw water faster than it can be recharged, the water table is lowered, creating a cone of depression. Any pollutant discharged onto the land will pollute water withdrawn by the well. Water withdrawal is taking water from the ground or surface to a place of use. Water consumption occurs when water that has been withdrawn is not returned to the surface water or ground water from which it came so that it may be used again in that area. The U.S. has the highest per capita water withdrawal rate in the world (41% is used to irrigate crops), followed by Canada with 20% of the world’s freshwater supply. In the western U.S. irrigation accounts for 85% of all water use. Water withdrawal for energy production and industrial use is highest in Europe and North America. For example, It takes 100,000 gallons to make an automobile, 1,000 gallons to produce 1 pound of aluminum, and 800 gallons to produce 1 pound of grain-fed beef in a feedlot. TOO LITTLE WATER Droughts cause more damage and suffering worldwide than any other natural hazard. Areas likely to face increased water shortages in the 1990s and beyond include northern Africa, parts of India, northern China, much of the Middle East, Mexico, parts of the western United States, Poland, and Russia. TOO MUCH WATER In India, for example, 90% of the annual precipitation falls between June and September, the monsoon season. This downpour causes floods, waterloggs soils, leaches soil nutrients, and washes away topsoil and crops. Hurricanes and typhoons can flood low- lying coastal areas. Prolonged rains anywhere cans cause streams and lakes to overflow and flood the surrounding land, but low-lying river basins are especially vulnerable. Floods, like droughts, are usually called natural disasters, but human activities have contributed to the sharp rise in flood deaths and damages since in 1960s. Cultivation of land, deforestation, overgrazing, and mining have removed water-absorbing vegetation and soil. Urbanization also increases flooding with highways, parking lots, and buildings that lead to rapid runoff of rainwater. Flood damage can be prevented or reduced by reforestation, rechannelization, dams, artificial levees, and floodplain management. WATER FAR FROM PEOPLE In some countries the largest rivers, which carry most of the runoff, are far from agricultural and population centers where the water is needed. Strategies for capturing some of this water and bringing water to people include building dams and reservoirs and using aqueducts to transfer water to other areas. The U.S. has plenty of fresh water. But much of it is in the wrong place at the wrong time or is contaminated. In the East the largest uses for water are energy production, cooling, and manufacturing. In the West the largest use is irrigation. In many parts of the eastern U.S. the most serious water problems are flooding, some urban shortages, and pollution. CONTAMINATED DRINKING WATER Not only is water becoming more scarce, its quality is also being degraded. Rivers are polluted. Aquifers are becoming contaminated with pesticides, fertilizers, and hazardous organic chemicals. In its passage through the hydrologic cycle, water is polluted by: · Sediment washed from the land by farming activities, forestry, mining, grazing, and construction · Excess nutrients from soil erosion, human and animal waste, and effluents from sewage treatment plants, causing algae blooms that use up dissolved oxygen and disrupt aquatic communities · Pathogens from sewage and livestock wastes · Hazardous chemicals produced by industrialized societies METHODS FOR MANAGING WATER RESOURCES One way to manage water resources is to increase the supply in a particular area by building dams and reservoirs, bringing in surface water from another area, or tapping groundwater. The other approach is to improve the efficiency of water use. Rainwater and snowmelt can be captured and stored in reservoirs created by damming streams. This water can be used to produce hydroelectric power, irrigate land, control flooding, and provide water carried by aqueducts to cities. Reservoirs are also used for recreation activities such as swimming, fishing, and boating. About 13.5% of the electrical power used in the U.S. is hydroelectric. Building small dams, which have fewer destructive effects than large dams and reservoirs, is a useful way to trap water for irrigation. TAPPING GROUNDWATER In the United States 23% of all fresh water used is groundwater. About half of the country’s drinking water (96% in rural areas and 20% in urban areas) and 40% of irrigation water are pumped from aquifers. Overuse of groundwater can cause or intensify several problems: aquifer depletion, subsidence, and intrusion of salt water into aquifers. Groundwater can also become contaminated. Currently about one-fourth of the groundwater withdrawn in the United States is not replenished. The most serious overdraft is in parts of the huge Ogallala Aquifer, extending from northern Nebraska to northwestern Texas. Ways to slow groundwater depletion include 1) control population growth, 2) not growing water thirsty crops in dry areas, 3) developing crop strains that require less water, and (4) wasting less irrigation water. Desalination (removing salts from ocean water or brackish (slightly salty) groundwater) is another way to increase freshwater supplies. Distillation and reverse osmosis are the two most widely used methods. Distillation involves heating salt water until it evaporates and condenses as fresh water, leaving salts behind in solid form. In reverse osmosis salt water is pumped at high pressure through a thin membrane whose pores allow water molecules but not dissolved salts to pass through. These plants provide less than 0.1% of the world’s water. Desalination, however, has a downside. It uses vast amounts of electricity and therefore costs three to five times more than water from conventional sources. Moreover, desalination produces large quantities of brine with high levels of salt and other minerals that must go somewhere. CLOUD SEEDING AND TOWING ICEBERGS Several countries, particularly the U.S. have been experimenting for years with seeding clouds with chemicals to produce more rain. Cloud seeding involves injecting a cloud with a powdered chemical such as silver iodide from a plane. Small water droplets in the cloud clump together around tiny particles of the chemical and form drops or ice particles large enough to fall as precipitation. There also have been proposals to tow massive icebergs to arid coastal areas (such as Saudi Arabia and southern California) and pump the fresh water from the melting bergs ashore. However, the technology for doing this is not available and the costs may be too high, especially for water-short LDCs. The U.S., the world’s largest user of water, wastes 50% of the water it withdraws. Worldwide, 65-70% of the water people use is wasted through evaporation, leaks, and other losses. A prime cause of water waste in the United States (and in most countries) is artificially low water prices. Cheap water is the only reason that farmers in Arizona and southern California can grow water-thirsty crops like alfalfa in the middle of the desert. It also enables people in Palm Springs, California, to keep their lawns and 74 golf courses green in a desert area. Water subsidies are paid for by all taxpayers in higher taxes. Because these external costs don’t show up on monthly water bills, consumers have little incentive to use less water or to install water-conserving devices and processes. Raising the price of water to reflect its true cost would be a powerful incentive for using water more efficiently. WATER RIGHTS IN THE UNITED STATES Laws regulating surface-water access and use differ in the eastern and western parts of the United States. In most of the East water use is based on the doctrine of riparian rights. Basically this system of water law gives anyone whose land adjoins a flowing stream the right to use water from the stream as long as some is left for downstream landowners. However, as population and water-intensive land uses grow, there often is not enough water to meet the needs of all the people along a stream. In the dry West the riparian system does not work because large amounts of water are needed in areas far from major surface-water sources. In most of this region the principle of prior appropriation regulates water use. In this first-come, first-served approach, the first user of water from a stream establishes a legal right for continued use of the amount originally withdrawn. If there is a shortage, later users are cut off in order, one by one, until there is enough water to satisfy the demands of the earlier users. Some states have a combination of riparian and prior appropriation water rights. To retain their prior appropriation rights, users must withdraw a certain amount of water even if they don’t need it (a use-it-or-lose-it approach) which discourages farmers from adopting water-conserving methods. However, this use-it-or-lose-it rule does not apply to water bodies shared by two or more states. Water allocation between states is determined by interstate compacts and court decrees. Most groundwater use is based on common law, which holds that subsurface water belongs to whoever owns the land above such water. This means that landowners can withdraw as much as they want to use on their land. When many users tap the same aquifer, that aquifer becomes a common-property resource. Unfortunately multiple users may remove water faster than it is replaced. The largest users have little incentive to conserve and can deplete the aquifer, creating another tragedy of the commons. Environmentalists and many economists call for a change in laws allocating water rights, with emphasis on water marketing. They believe the farmers and other users that save water throughout conservation or a shift to less water-thirty their crops should be able to sell or lease the water the save to industries and cities rather than losing their right to this water. WASTING LESS WATER In the United States, industry is the largest conserver of water. However, the potential for water recycling in U.S. manufacturing has hardly been tapped because the cost of water to many industries is subsidized. Flushing toilets, washing hands, and bathing account for almost 78% of the water used in a typical U.S. home. Leaks waste 20-35% of water withdrawn from public supplies in the U.S. Large quantities of water are used to clean sidewalks and streets and to irrigate lawns and golf courses. Many cities offer no incentive to reduce leaks and waste. In New York City, for example, 95% of residential units don’t have water meters. Users are charged flat rates, with the average family paying less than $100 a year for unlimited use of water. CASE STUDY: THE SHRINKING OGALLALA AQUIFER The Ogallala, the worlds largest known aquifer, underlies the Great Plains. Water pumped from the Ogallala transformed the prairie into America’s most productive farmland. The aquifer is essentially a nonrenewable fossil aquifer with an extreamly low recharge rate. Water is being pumped out at eight times its natural recharge rate, mostly for irrigation to supply 15% of our corn and wheat, 25% of our cotton and 40% of our feedlot beef. The withdrawal rate is 100 times the recharge rate for parts of the aquifer that lie beneath Texas, New Mexico, Oklahoma, and Colorado. At the present rate of withdrawal, one fourth of the aquifer’s original supply will be depleted by 2020. Depletion is encouraged by federal tax laws that allow farmers and ranchers to deduct the cost of drilling equipment and sinking of wells. Long before the water is gone, the high cost of pumping water from a rapidly dropping water table will force many farmers to grow “water-miser” crops instead of profitable but “thirsty” crops such as cotton and sugar beets. Some farmers will go out of business. Total irrigated area is already declining in five of the seven states using this aquifer because water must be pumped from depths as great as 1,830 meters (6,000 feet). If farmers in the Ogallala region conserved more water and switched to low-water crops, depletion of the aquifer could be delayed. CASE STUDY: WATER RIGHTS IN THE UNITED STATES Laws regulating surface-water access and use differ in the eastern and western United States. In most of the East water use is based on the doctrine of riparian rights. Basically this system of water law gives anyone whose land adjoins a flowing stream the right to use water from the stream as long as some is left for downstream landowners. However, as population and water-intensive land uses grow, there often is not enough water to meet the needs of all the people along a stream. In the arid and semiarid West the riparian system does not work because large amounts of water are needed in areas far from major surface-water sources. In most of this region the principle of prior appropriation regulates water use. In this first-come, first-served approach, the first user of water from a stream establishes a legal right for continued use of the amount originally withdrawn. If there is a shortage, later users are cut off in order, one by one, until there is enough water to satisfy the demands of the earlier users. Some states have a combination of riparian and prior appropriation water rights. To retain their prior appropriation rights, users within a particular state must withdraw a certain amount of water even if they don’t need it--a use-it-or-lose-it approach--which discourages farmers from adopting water-conserving irrigation methods. However, this use-it-or-lose-it rule does not apply to water bodies shared by two or more states. Water allocation between states is determined by interstate compacts and court decrees. Most groundwater use is based on common law, which holds that subsurface water belongs to whoever owns the land above such water. This means that landowners can withdraw as much as they want to use on their land. When groundwater users tap the same aquifier, that aquifier becomes a common-property resource. Unfortunately multiple users may remove water faster thatn it is replaced. The largest users have little incentive to conserve and can deplete the aquifer for everyone, creating another tragedy of the commons. Enviromentalists and many economists call for a change in laws allocating rights to surface and groundwater supplies, with emphasis on water marketing. they believe that farmers and other users who save water-thirsty crops should be able to sell or lease the water tthey save to industries and cities rather than losing their rights to this water.
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