tant reason that separate sewers, even though more expensive, are favored by public health officials. The biologic processes can also be severely affected by toxic industrial waste that can kill the “good” bacteria, which are crucial to the treatment process. Accord- ingly, many communities require pretreatment for industrial wastes. Tertiary treatment is the most advanced form of waste treatment. It includes a number of practices such as the use of ozone, which is a strong oxidizing agent, to remove most of the remaining BOD, odor, and taste, and the addition of alum as a phosphate precipitator. A recent and innovative method of ter- tiary treatment is to spray chlorinated effluent on ei- ther croplands, wooded areas, or mine tailings after it has beengivensecondary treatment.This method has several distinct advantages over the traditional direct discharge of the effluent into surface watercourses. First, biologic digestion in the soil removes almost all of the remaining BOD. Second, soil and plants are capable of absorbing large amounts of nitro- gen and phosphorus during the growing season, which slows their release into the environment. Other benefits include increased crop and timber yields and groundwater recharge. The land area needed to handle treated wastewater by the spray irrigation method is approximately 6.4 square ki- lometers per 100,000 people. Wastewater Disposal in Rural and Suburban Areas In areas where population densities are less than about 1,000 people per square kilometer,the cost of a sewer systemand treatment plant are difficult to justify. Septic systems are commonly used in residential areas for disposal of domestic waste- waters. Household effluent is piped to a buried septic tank, which acts as a small sedimentation basin and anaerobic (without oxygen) sludge di- gestion facility. The effluent exits from this tank into a disposal field where aerobic (with oxygen) biologic breakdown of dissolved and solid or- ganic compounds occurs. In order to operate ef- fectively, the soil must be of sufficient depth and permeability so that microbial decomposition can take placeprior to the effluent reachingthe water table. The Environmental Protection Agency esti- mates that 25 percent of the homes in the United States use some form of a septic disposal system. Robert M. Hordon Further Reading American Water Works Association, and American Society of Civil Engineers. Water Treatment Plant De- sign. Editedby Edward E.Baruth. 4th ed.New York: McGraw-Hill, 2005. Drinan, Joanne E. Water and Wastewater Treatment: A Guide for theNonengineering Professional. BocaRaton, Fla.: Lewis, 2001. Gray, N. F. Biology of Wastewater Treatment. 2d ed. Lon- don: Imperial College Press, 2004. Hammer, Mark J., and Mark J. Hammer, Jr. Water and Wastewater Technology. 6th ed. Upper Saddle River, N.J.: Pearson/Prentice Hall, 2008. McGhee, Terence J. Water Supply and Sewerage. 6th ed. New York: McGraw-Hill, 1991. Metcalf & Eddy, Inc. Wastewater Engineering: Treatment and Reuse. 4th ed. Revised by George Tchoban- oglous, Franklin L. Burton, and H. David Stensel. Boston: McGraw-Hill, 2003. 1306 • Waste management and sewage disposal Global Resources Paper & paperboard products 32.7% Yard wastes 12.8% Food wastes 12.5% Plastics 12.1% Metals 8.2% Rubber, leather, & textiles 7.6% Wood 5.6% Glass 5.3% Other 3.2% Source: Municipal Solid Waste in the United States: 2007 Facts and Figures Note: U.S. Environmental Protection Agency, . Total U.S. municipal solid waste generated in 2007 was about 230 million metric tons, or 2.1 kilograms per person per day. Not included in these figures are mining, agriculture, industrial, and construction wastes; junked automobiles and equipment; or sewage. U.S. Municipal Solid Waste, 2007 Qasim, Syed R. Wastewater Treatment Plants: Planning, Design, and Operation. 2d ed. Lancaster, Pa.: Tech- nomic, 1999. Laak, Rein. Wastewater Engineering Design for Unsewered Areas. 2d ed. Lancaster, Pa.: Technomic, 1986. Tillman, GlennM. Water Treatment: Troubleshootingand Problem Solving. Chelsea, Mich.: Ann Arbor Press, 1996. See also: Clean Water Act; Environmental engineer- ing; Environmental Protection Agency; Eutrophica- tion; Solid waste management; Streams and rivers; Water pollution and water pollution control; Water supply systems. Water Categories: Ecological resources; energy resources; mineral and other nonliving resources Water is an odorless, tasteless, and transparent com- pound that isa critical factor in allchemical, physical, and biological processes. As far as is known, water ex- ists freely and in great abundance on only one planet in our solar system, Earth. Background Although water could exist on the Earth without life, life could not exist without water. It is the most abun- dant liquid on the Earth. In its solid and liquid forms, water coversabout 70percent oftheEarth’s surface. It exists in gaseous form as water vapor in the lower at- mosphere, varying from close to 0 percent to about 4 percent by volume from region to region. Water constitutes most of the living tissue in humans: about 92 percent of blood plasma, 80 percent of muscle tissue, 60 percent of red blood cells, and more than 50 percent of most other tissues. Water Properties Water is a compound of two atoms of hydrogen and one of oxygen, giving it the well-known chemical for- mula H 2 O. It has some unique properties. It can exist naturally in three states on Earth: solid, liquid, and gaseous. Furthermore, under normal pressure, when heated from 0° Celsius, the melting point of water, to 4° Celsius, it contracts and reaches its highest density. This unusual thermal condition contrasts sharply with most other substances, which expand and experience decreasing density when they are heated. Therefore, ice is less dense than water and will float. This prop- erty has substantial implications, as it allows water to freeze from the surface downward, thereby allowing circulation to continue under the frozen surface so that fish cansurvive. Submarines that travel underthe Arctic Ocean ice pack could not do so were it not for water’s unusual thermal property. Water is anexcellent solvent, so much sothat “pure water” is hard to find in nature. Water has the highest specific heat of all common substances. Specific heat is the amount of heat that a fluid needs to raise the temperature of a unit volume by 1 degree. This is an important property, as the enormous heat capacity of water has an equalizing effect on the Earth’s climate. Global Resources Water • 1307 A Salvadoran boyuses water froma common faucetto bathe himself. (AP/Wide World Photos) Maritime locations have a milder climate than those that are located in continental interiors. Thus, the av- erage annual temperature range between the warm- est and coldest months for Winnipeg, Canada, and the Isles of Scilly, England, is 39° and 8.3° Celsius, re- spectively. Even though both places are at 50° north latitude, the temperatures in the Isles of Scilly are moderated by their oceanic location, whereas Winni- peg is in the middle of a large continent. The high heatcapacity of water is closelyassociated with some other unusual properties of water, namely, the latent heat of fusion and vaporization. The latent heat of fusion is the amount of heat per unit mass (80 calories per gram) that is necessary to change a sub- stance completely at itsmelting point to a liquid at the same temperature. This means that if heat is applied to ice at 0° Celsius, the temperature of the ice remains constant until all of the ice has melted. Note that the term “latent” indicates a change in state without a change in temperature. In a similar manner, the la- tent heat of vaporization is the amount of heat per unit mass (539 calories per gram) required to change a liquid completely at its boiling point to a gas at the same temperature. This means that if heat is applied to water at 100° Celsius, the water begins to boil and the temperature remains the same until all the water has boiled away. The old saying “a watched pot never boils” reflects the fact that water needs an enormous amount of heat before it can reach its boiling point and undergo a phase change from liquid to vapor. The processes of fusion and vaporization are revers- ible and thereby represent two of the most important energy transformations in the environment, as they strongly influence the Earth’s climate. Water boils at 100° Celsius at sea-level pressure, which is one of the highest boiling points of any fluid on Earth. This property differs from the general rule that the boiling point of a fluid goes up as its molecu- lar weight increases. This rule does not apply to water that has a relatively low molecular weight. Viscosity in- creases with increasing pressure for nearly all fluids. This is not the case with water, for which viscosity de- creases as pressure increases. This property explains why water, which is under high pressure in a water- distribution system, is able to flow, rather than drib- ble, out of a kitchen tap. The hydrogen bonding of water allows its surface tension to be two to three times greater than that of most common liquids. This property explains why certain insects can “walk on water” and why steel nee - dles canfloat. Surface tension(cohesion) andthe ten - dency of water to wet solid surfaces (adhesion) cause capillarity, which allows water to “climb” a wall or tube. If water had a much weaker or smaller surface tension (and therefore weaker capillary forces), soil water, which is necessary for plant life, would be un- able to overcome gravity. Distribution of Water Earth is a well-watered planet. Thus, hypothetically, if the entire surface of the Earth could be leveled off and the ocean depths filled with the continents, the planet wouldbe covered withwater to adepth of more than 3 kilometers.By far, most of theworld’swater (97 percent) is contained in the oceans. Another 2 per- cent is locked in ice caps and glaciers.This means that almost all the water in the world (99 percent) is either salty or frozen. The remaining water is accounted for by groundwater to a depth of 4 kilometers, freshwater lakes, saline lakes and inland seas, soil moisture and water in the unsaturated zone, and the atmosphere. Finally, if one measured the average volume of all the rivers on Earth, the estimated amount would only be 0.0001 percent of the total water on the planet. Water as a Resource There are several characteristics that pertain to water as a resource. First, water is a renewable resource. As governed by the hydrologic cycle, it is continuously going through the processes of evaporation, convec- tion, and advection in the atmosphere; precipitation; interception and transpiration by vegetation; over- land flow; infiltration and percolation through the soil and unsaturated zone to the groundwater in shal- low, intermediate, and deep aquifers; and base flow from groundwater to streams for eventual transport to the ultimate sink on Earth, the oceans. In the oceans, it evaporates again to continue the cycle. The quantity of water on Earth is relatively fixed, although the quality is affected by numerous anthropogenic ac- tivities. Second, water is ubiquitous on the Earth. It can be found almost anywhere, although it may be too salty or frozen to use directly. Available and abundant freshwater resources, like mineral resources, are un- evenly distributed. Thus, water must be transported long distances to supply the needs of major metropol- itan areas. For example, New York City gets most of its water from Delaware River basin reservoirs, some 200 kilometers away.Los Angeles depends on water that is 1308 • Water Global Resources transported hundreds of kilometers from Northern California, the Owens Valley east of the Sierras, and the Colorado River. Third, water can be considered a common prop- erty that has poorly defined property rights. Even during droughts, when potential consumers may be excluded, water is sometimes treated as a free com- modity. Society recognizes the expenses associated with the diversion, treatment, and distribution of water but does not recognize the cost of the water it- self. The western United States stands out as a major exception to the common property concept, because ownership of water does occur, usually on a first- come, first-served basis. Fourth, water is relatively inexpensive (although in certain drought-prone regions, in the face of popula- tion growth, its scarcity is a growing concern). The combination of thecommon property aspect of water, water-supply technology, and economies of scale make water anunusually cheapcommodity even thoughit is essential for life and has no substitute. For example, treated public water in the United States delivered to a domestic user costs about 13 cents per liter (5 cents per gallon). Water Use The various ways that water is used can be dichoto- mized into offstream and instream use. Offstream use pertains to water that is diverted (withdrawn) from surface water or groundwater sources and trans- ported to the place of use. This includes water that is used for domestic, commercial, irrigation, livestock, industrial, mining, and thermoelectric power pur- poses. Each of these seven categories of offstream water use has a different effect on the potential for re- use of the return flows. For example, the return flow for irrigation is often contaminated bypesticides,her- bicides, salts, and fertilizers to such an extent that it has minimal reuse potential. An unfortunate illustra- tion of this situation occurs on the lower Colorado River near Yuma, Arizona, where the United States built a large desalinization plant in order to reduce the salinity of the water for the irrigated areas in nearby Mexico. The plant opened in 1992 and has ex- perienced numerous operating problems. In con- trast, the reuse potential of most of the water dis- charged from thermoelectric plants is high, because the major change in the water is an increase of tem- perature. Instream water use occurs without the water being diverted from surface or groundwater sources. These uses include navigation,low flow maintenance to ben- efit aquatic ecosystems, hydroelectric power genera- tion, and wastewater assimilation. Although instream uses have an impact on the quality and quantity of water resourcesfor all uses,numerical estimatesof the Global Resources Water • 1309 U.S. Water Use Per Day (billions of gallons) Year Total Per Capita (gallons) Irrigation Public Supply Rural Industrial & Misc. Steam Electric Utilities 1940 140 1,027 71 10 3.1 29 23 1950 180 1,185 89 14 3.6 37 40 1960 270 1,500 110 21 3.6 38 100 1970 370 1,815 130 27 4.5 47 170 1980 440 1,953 150 34 5.6 45 210 1990 408 1,620 137 41 7.9 30 195 1995 402 1,500 134 40 8.9 29 190 2000 408 1,430 137 43 9.2 23 196 Source: U.S. Department of Commerce, Statistical Abstract of the United States, 2004, 2004. Note: Per capita figures are gallons; all other values are in billions of gallons. amount of instream use are difficult to obtainwiththe exception of hydroelectric power generation. Diversion of freshwater resources varies consider- ably from country to country. One useful measure of existing or potential water shortages is to examine to- tal annual diversions as a percentage of the annual re- newable water supplies for that country. Some coun- tries, such as Canada (1.4 percent) and the United States (15.5 percent), are well within the limits of their overall renewable water supplies, although the drier areas of the Southwest are reaching the limits of local resources. Other countries in arid regions such as Libya (712 percent) and Saudi Arabia (722 percent) are clearly in excess of their renewable sup- plies and are therefore mining their groundwater reserves. Water-use data for the United States have been compiled at five-year intervals by the U.S. Geological Survey on a statewide basis since 1950. These five-year water-census reports provide an invaluable summary of water-use trends and patterns. As expected, total water withdrawals increased from 1950 to 1980 as the population increased. However, beginning in 1985 and contrary to expectations that water use would simply continue to increase as population increased, water use actually declined and then remained stable through 2000. It is hypothesized that technological changes, suchas irrigation practices,the introduction of low-flow toilets, and a growing awareness of water conservation, led to a more efficient use of water. Excluding water withdrawn for thermoelectric power, irrigation represents the largest use of fresh water in the United States, accounting for approxi- mately 65 percent of total water withdrawals. The three states with the largest irrigation withdrawals are California (22.4 percent), Idaho (12.5 percent), and Colorado (8.4 percent). In terms of source, surface water and groundwateraccountfor 76 percent and 24 percent, respectively, of the total amount of freshwa- ter withdrawals. Public watersupply pertains to thediversions made by public and private (investor-owned) systems that are deliveredto manyusersfor domestic(residential), commercial, industrial,and thermoelectric powerpur- poses. Surface water accounts for 63 percent of the total fresh water diverted by public water systems. It does not include industrial self-supplied water or the thousands of individual homes and farmsteads in the United States that have their own wells. About 15 per - cent of the U.S. population have their own wells. Even in the most densely populated state in the nation (New Jersey), theestimated portion of the population that has its own wells has remained at about 10 per- cent for several decades. Water Disputes Because water is essential for life, disputes over its use not only are numerous but also have been going on for several thousand years. In arid areas, such as the Middle East, water is crucial for irrigated agriculture. Thus, Turkey’s decision to build reservoirs for irriga- tion in the headwaters of the Tigris and Euphrates rivers, whichare initsterritory,may deprivethe down- stream states Iraq and Syria of water on which they have come to depend. The allocation of the waters of the Jordan River among the neighboring states of Is- rael, Jordan,Lebanon,and Syria inanother politically sensitive and drought-prone area is related to the via- bility of peace in the region. With the small exception of some limited reserves of groundwater that accrued from ancient pluvial periods, Egypt is totally depen- dent on the Nile River, which originates in Ethiopia and Lakes Albert and Victoria in east-central Africa. Any large diversion of the Nile by the upstream states would have a major impact on Egypt. The Colorado River and its tributaries begin in the Rocky Mountains in Wyoming, Colorado, and New Mexico and flow for 2,333 kilometers through Utah, Arizona, Nevada,and California beforeemptying into the Gulf of California in Mexico. Although agree- ments exist among the seven states and Mexico re- garding water allocation, problems have developed and are likely to worsen in the future, because the ini- tial allocation was predicated on an average flow that was based on an above-normal precipitation cycle. In the face of drier or more normal precipitation cycles, the allocations have to bereduced, with obvious harm to the large users in the basin, particularly those who use the water for irrigation. The Chicago diversion scheme provides a good ex- ample of an international agreement on water alloca- tion that wassettled amicably.As Chicago grewduring the late nineteenth century, drinking water was ob- tained from a nearby and abundant source, Lake Michigan. Serious health problems developed when Chicago’ssewage was sentback to thesame lake. Inor- der to maintain the quality of the drinking water, the Chicago Sanitary and Ship Canal was connected with the Illinois River, which flows into the Mississippi River. Because excessive out-of-basin diversions from 1310 • Water Global Resources Lake Michigan would affect navigation farther down - stream at Montreal and Quebec on the St. Lawrence River, an international agreement between Canada and the United States was reached early in the twenti- eth century that allowed a diversion of 85 cubic me- ters per second. Water Quality Until relatively recently, societies were more con- cerned with water quantity than with water quality. However, this began to change as growing concen- trations of industry and increased population density led to larger amounts of impurities being released into local water sources. By the end of the nineteenth century, the Thames River near London and other rivers near large European cities were so polluted that the rivers became anaerobic (containing no dis- solved oxygen)and emitted offensive odors. Fishcould not survive in these waters. It became obvious that wastewater from residential and commercial sources had to be treated prior to release into a receiving watercourse. One solution to the problem in urban areas has been to construct public sewers that connect to waste- water treatment plants,which have helped to improve water quality. In more rural areas, septic systems and well-constructed latrines are generally used to handle wastewater. However,there are countrieswhere unim- proved sanitation facilities, such as public and open- pit latrines, are used by large segments of the popula- tion. Thus, access to improved sanitation for the total population (urban and rural) varies from an esti- mated low of 9 percent for Chad and Eritrea in Africa to 100 percent forsuchcountries as Canada, Israel, Ja- pan, and the United States. The types of water pollution can be categorized on the basis of their effect on human health andtheenvi- ronment. Organic wastes are decomposed by chemi- cal and biological processes that can use up the dis- solved oxygen in water that is essential for fish and other aquatic organisms. Excessive amounts of ni- trates and phosphates entering surface waters can lead to accelerated aquatic plant growth and organic debris buildup, a process known as eutrophication. Sediments from agricultural and urban land uses can cover benthic (bottom) organisms, clog steam chan- nels, and destroy certain aquatic organisms. Bacteria and viruses that come from animal and human wastes can enter drinking water supplies and cause such dis - eases as dysentery,hepatitis, and cholera. Heavy metals such as lead and mercury, fibers such as asbestos, and industrial acids are harmful to humans and aquatic ecosystems. Synthetic organic compounds that in- clude water-soluble materials (cleaning compounds and insecticides) and insoluble materials (plastics and petroleum residues) can cause a variety of ail- ments in humans and animals, such as kidney disor- ders, birth defects, and possibly cancer. Radioactive wastes from commercial and military sources release toxic radiation that causes cancer. Thermal pollution results from heated water being discharged into re- ceiving watercourses, usually from power plants. The additional heat can lead to species change and in- creased growth rates in many types of aquatic organ- isms. As if the foregoing list were not extensive enough, an additional problem has developed with the discov- ery that endocrine-disrupting compounds (pharma- ceuticals) and personal care products, collectively known as (PPCPs), can be excreted from humans and livestock (animals that are given food additives such as antibiotics, growth promoters, and pharmaceuti- cals). The array of PPCPs that have been detected in drinking water sources include antibiotics, painkill- ers, beta-blockers, and sex steroids. The majority of the PPCPs wind up in wastewater treatment plants, where they are only partially removed by existing technology. The remaining PPCPs end up in surface streams from overland runoff or get directly into groundwater from septic systems. Currently, there is minimal change in drinking water legislation regard- ing these products by government regulatory bodies, although there isgrowing recognitionthatan increas- ing amount of PPCPsare entering drinking water sup- plies without humans’ full knowledge of the dangers to health. Water pollution sources are often dichotomized as point and nonpoint. Point sources of pollution refer to a known discharge point or outfall from a facility such as a wastewater treatment plant. Although these are individually important, most of the stream pollu- tion comes from nonpoint sources, which are diffuse and scattered throughout the landscape. Nonpoint sources include storm-water runoff from urbanized areas and agricultural runoff from rural areas. Many contaminants from agricultural operations (herbi- cides and pesticides) are adsorbed onto soil particles, which are washed into the stream during storm events and transported downstream. Robert M. Hordon Global Resources Water • 1311 Further Reading Brooks, Kenneth N. Hydrology and the Management of Watersheds. 3d ed. Ames: Iowa State University Press, 2003. Cech, Thomas V. Principles of Water Resources: History, Development, Management, and Policy.2ded. Hoboken, N.J.: John Wiley & Sons, 2005. Chapelle, Frank. Wellsprings: A Natural History of Bot- tled Spring Waters. New Brunswick, N.J.: Rutgers University Press, 2005. Clarke, Robin, and Jannet King. The Water Atlas. New York: New Press, 2004. De Villiers, Marq. Water: The Fate of Our Most Precious Resource. Boston: Houghton Mifflin, 2000. Gleick, Peter H., et al. The World’s Water, 2008-2009: The Biennial Report on Freshwater Resources. Washing- ton, D.C.: Island Press, 2009. Glennon, Robert Jerome. Water Follies: Groundwater Pumping and the Fate of America’s Fresh Waters. Wash- ington, D.C.: Island Press, 2002. Hunt, Constance Elizabeth. Thirsty Planet: Strategies for Sustainable Water Management. New York: Zed Books, 2004. Hutson, Susan S., et al. Estimated Use of Water in the United States in 2000. Reston, Va.: U.S. Geological Survey, 2004. Manning, John C. Applied Principles of Hydrology. Illus- trated by Natalie J. Weiskal. 3d ed. Upper Saddle River, N.J.: Prentice Hall, 1997. Powell, James L. Dead Pool: Lake Powell, Global Warming, and theFuture of Waterin theWest.Berkeley: University of California Press, 2008. Spellman, Frank R. The Science of Water: Concepts and Applications. 2d ed. Boca Raton, Fla.: CRC Press, 2008. United Nations World WaterAssessment Programme. Water: A Shared Responsibility. New York: Berghahn Books, 2006. Ward, Andrew D., and Stanley W. Trimble. Environ- mental Hydrology. 2d ed. Boca Raton, Fla.: Lewis, 2004. Whiteley, John M., Helen M. Ingram, and Richard Warren Perry, eds. Water, Place, and Equity. Cam- bridge, Mass.: MIT Press, 2008. Web Site U.S. Geological Survey Water Science for Schools http://ga.water.usgs.gov/edu/ See also: Deep drilling projects; ElNiño andLa Niña; Eutrophication; Groundwater; Hydroenergy; Hydrol- ogy and the hydrologic cycle; Irrigation; Lakes; Mon- soons; Oceans; Streams andrivers;Thermal pollution and thermal pollution control; United Nations Con- vention to Combat Desertification; Water pollution and water pollution control. Water pollution and water pollution control Category: Pollution and waste disposal Water may become polluted by humans above the con- centrations of constituents normally produced by the dissolution of minerals, the atmosphere, and the bio- sphere. High concentrations of toxic materials such as benzene, lead,and mercury may posemajor health con- cerns. Thetoxic constituents in naturalwaters must be reduced in concentration by chemical or physical pro- cesses known as remediation processes. Major issues include decisions as to the desirable levels of pollution reduction and who should pay for the cleanup. Background There are natural cycles of water compositional change that are not considered pollution. Most pre- cipitation contains only tiny amounts of dissolved constituents obtained from the atmosphere, except for a relatively high concentration of carbon dioxide in the form of carbonic acid. Precipitation may also pick up small amounts of dissolved constituents as it moves through plants. As the water from the precipi- tation moves through the soil, the soil becomes more acidic from the carbon dioxide in the soil. This acid water can dissolve the common constituents found in minerals so the water becomes enriched in calcium, magnesium, potassium, sodium, chloride, sulfate, and a complex ion formed from the carbonic acid, bicar- bonate. Theseconstituentsare healthful toorganisms as long as they remain in low concentrations. Other constituents arepresent inonlytiny quantitiesinmost minerals so that they are present in water in only dilute concentrations. Natural organic compounds from the decomposition of plants and animals may also become dissolved in water. 1312 • Water pollution and water pollution control Global Resources Groundwater The soilwater maymovefarther down intopermeable rocks (rocks through which water readily flows) such as sandstones (rocks composed mostly of sand) or limestones (composed mostly of calcium carbonate). This deeper water is called groundwater. If the ground- water encounters other soluble minerals, then the water composition may gradually change. For exam- ple, if groundwater encounters the soluble mineral gypsum (a calcium sulfate mineral), it produces wa- ters with high concentrations of calcium and sulfate up to the point at whichnomore gypsum will dissolve. If the groundwater encounters a much more soluble mineral such as halite (a sodium chloride mineral), the water can become enriched in sodium and chlo- ride. Most deep groundwaters have high concentra- tions of sodium, chloride, calcium, and sulfate, sug- gesting contact with halite and gypsum, which make it unfit to drink or to use in irrigation. Even shallow groundwaters in some places in central Kansas be- come contaminated with near-surface gypsum and halite. Groundwater may encounter rarer minerals such as iron, lead, mercury, and zinc minerals combined with sulfur, which react and produce acid waters with high concentrations of the toxic metals. This process may be accelerated by mining: The chemically reac- tive mineralsmay be exposed toair and waterand may dissolve even more rapidly than if left unmined below the surface. Pollution Mining may expose fine minerals so that weathering processes may more rapidly decompose the minerals. Industrial processes produce a plethora of toxic con- stituents, including mercury, lead, arsenic, cadmium, chromium, nitrate, selenium, radioactive materials, and hydrocarbons (organic compounds composed of hydrogen, carbon, and often oxygen, nitrogen, or sul- fur). Pollutants such as mercury become concen- trated in the food chain and can produce serious problems in humans. For example, a number of peo- ple were poisoned by mercury near Minamata, Japan, in the 1950’s. Industrial waste enriched in mercury was dumped into the bay, where it was concentrated by shellfish that people ate. People in many areas of the world have been poisoned by drinking water from lead pipes. If the water passing through the pipes is moderately acidic, the water dissolves the lead. In Nova Scotia, arsenic polluted groundwater to a con - centration of up to 5 milligrams of arsenic per liter as a result of an arsenic mineral being discarded in gold- mining waste piles. There are also hundreds of hydrocarbon com- pounds produced by industry on the list of potential carcinogenic substances which are not desirable to have in any amount in drinking water. The maximum concentration of toxic elements or compounds al- lowed in drinking water in the United States is set by the Environmental Protection Agency (EPA). Some toxic organic compounds, such as benzene, are relatively insoluble in water. Benzene can move from the water as a separate liquid if there is consid- erable benzene present (much as oil and water can separate when they are mixed together). Some com- pounds—again, benzene is a good example—are vol- atile, as they readily vaporize from the liquid. Thus a volatile, benzene-type liquid under buildings can pro- duce a vapor that migrates and concentrates in the basements of the buildings. Other hydrocarbon com- pounds, such as alcohols, are relatively soluble in water, so considerable amounts of these hydrocar- bons may move dissolved in groundwater. Health effects as a result of exposure of these toxic substances are varied. Some, such as arsenic, chro- mium, mercury, lead, and many organic compounds, are carcinogens. Chromium may also cause skin ul - cers. Mercury can causefatigueand energy loss. Lead, which ishighly toxic,inhibits hemoglobinformation. Global Resources Water pollution and water pollution control • 1313 U.S. Drinking Water: Maximum Allowed Concentrations of Key Toxic Compounds Constituent Milligrams per Liter Arsenic 0.010 Atrazine (pesticide) 0.003 Benzene (volatile organic) 0.005 Cadmium 0.005 Chromium 0.1 Cyanide 0.2 Lead 0.015 Mercury 0.002 Pentachlorophenol 0.001 Selenium 0.05 Water Pollution Control Water pollution can be controlled by passive and ac- tive methods. Passive methods include the storage of hazardous wastes under conditions that reduce the movement of toxic constituents into the groundwater system. Ideal storage would be in areas of low rainfall with little population in rocks of low permeability so that the toxic constituents remain in place. Rocks of low permeability include unfractured mudrocks and many igneous and metamorphic rocks. For example, high levels of radioactive waste materials become ex- tremely hot and are highly corrosive. Much of the ra- dioactive material in these high-level wastes will take hundreds of thousands of years to decay. Plutonium, for example, concentrates in the bones of vertebrates and takes more than 240,000 years to decay. Thus, al- ternative long-term storage must be found. It is not economically feasible to transport house- hold or industrial garbage very far, so local landfills must accommodate much of this waste unless itisvery hazardous. No one wants these landfills nearby, so large cities incur significant expense to their moun- tains of garbage. Moreover, rainfall is high in the cen- tral and eastern United States, so it is important to iso- late waste physically from the groundwater (ideally by storing it where there are impermeable rocks), since rain will infiltrate and move the soluble materials into the groundwater. Unfortunately, many old landfills were sited in permeable rocks or in sediment such as sands and gravels in river floodplains in which groundwater moves directly through the landfill. The locations of many old, unuseddumps or landfills have been forgotten, so they continue their slow pollution of the groundwater. Moreactivemethods mustbe usedto controlpollu- tion in cases where groundwater or soil has already been contaminated. One problem is determining who will pay for the expensive cleanup or remediation. If a specific industrial polluter is identifiable, the sus- pected polluter usually must be sued. The industry will have to pay for cleanup if it is proved to have caused the pollution. If no industry can be responsible, then individual landowners or the government may have to pay for the remediation. Exceedingly widespread or hazardous cases of pollution may become EPA Superfund cleanup sites if no industry or other gov- ernment agency canbe heldliable forthepollution. Every cleanup site is different in terms of pollut - ants, geology, and precipitation, so a variety of meth - ods must be used. One method is to remove all the contaminated material physically and move it to a better landfill. Organic compounds that evaporate may be removed to the air by pumping the polluted water fromthe ground andvaporizing it ina chamber. This procedure is not used frequently,as it simply pol- lutes the air instead of the water. Some organic com- pounds may be removed by carbon filters, although this is expensive. Industrial organic compounds may be burned at high temperature instead of buried to form harmless carbon dioxide and water. Large vol- umes of soils or groundwater contaminated by petro- leum products may be aerated with nutrients and mi- crobes so that the organisms change the petroleum to harmless materials. Removal of multiple contaminants from waters may involve many processes in combination that re- move specific contaminants. Besides the methods dis- cussed above, such processes include chemical precipi- tations of insoluble solids, exchange of contaminants onto special resins, and filtration of contaminants. History of Legislation in the United States During the industrialization of the United States in the nineteenth century,garbage andsewage were allowed to collect in streets and near water supplies and were dumped untreated into rivers. This led to epidemics of diseases spread by water, such as cholera, hepatitis, and typhoidfever.The RiversandHarbors Actof1899 prohibited the dumping of trash into bodies of water. In the latter part of the nineteenth century, some cit- ies began to filter their water supplies through sand. By the beginning of the twentieth century, drinking water had begun to be chlorinated to kill harmful or- ganisms. Thus, by the mid-twentieth century, disease spread by water became rare in the United States, and the focus of pollution control began to shift to chemi- cal wastes. Public awareness began to increase because of well-publicized problems produced by pollution such as fish kills, human illness (such as the mercury poisioning that occurred at Minamata Bay, Japan), and lakes choked by abundant plant growth. Excessive plant growth may be produced by exces- sive nitrogen and phosphorous nutrients in waters. Algae, for example, may cover much of a lake’s sur- face, producing foul-smelling water and using up the dissolved oxygen from the water as the algae die and decay. With insufficient oxygen, fish may begin to die rapidly. The first real response by the federal government to the need for water pollution control was the Fed - 1314 • Water pollution and water pollution control Global Resources eral Water Pollution Control Act of 1948. This weak law stated that the states were responsible for water quality and that the federal government would inter- vene only if the states could not resolve issues of inter- state pollution. The original act was extended in 1956 and 1961, and some of the original weaknesses were addressed. For example, money was included to help states and towns fund water treatment plants. As a response to growing pollution problems, the federal government passed the Federal Water Quality Act of 1965, commonlyknown as the Clean WaterAct, in which thefederal government took theresponsibil- ity for water pollution control. The enforcement of the law involvedvariousfederal agencies until it wound up with the Environmental Protection Agency in 1970. According to this act the states were supposed to de- velop criteria and enforcement policies regarding water quality, but they were slow to do so. Therefore the Water Quality Act of 1970 was passed; it strength- ened federal control ofdischarges ofhazardous wastes. Federal grants were given to some industries for treat- ment control of pollutants. The Water Pollution Control Act of 1972 was the first law that gave the federal government the power to set minimum standards for water quality and to re- quire strict enforcement of these standards through the EPA. It became illegal to discharge any pollutant into a stream unless a permit was obtained. Violations were enforced bylarge dailyfines. Some rivers,such as the Willamette River in Oregon, have made incredi- ble recoveries as a result of these laws. The Willamette River changed from a foul-smelling, organic-rich sewer in which few fish could survive into a healthy, oxygen-rich river with abundant fish. Beginning in the 1970’s the list of organic chemicals not allowed in U.S. streams and lakes increased to many hundreds of compounds. Robert L. Cullers Further Reading Baker, Katherine H., and Diane S. Herson, eds. Biore- mediation. New York: McGraw-Hill, 1994. Boulding, J. Russell, and Jon S. Ginn. Practical Hand- book of Soil, Vadose Zone, and Ground-Water Contami- nation: Assessment, Prevention, and Remediation.2d ed. Boca Raton, Fla.: Lewis, 2004. Palmer, Christopher M. Principles of Contaminant Hy- drogeology. 2d ed. Boca Raton, Fla.: CRC Press/ Lewis, 1996. Perk, Marcel van der. Soil and Water Contamination: From Molecular to Catchment Scale. New York: Taylor & Francis, 2006. Smol, John P. Pollution of Lakes and Rivers: A Paleoenvi- ronmental Perspective. 2d ed. Hoboken, N.J.: Wiley- Blackwell, 2008. Spellman, Frank R. “Water Pollution.” In The Science of Water: Concepts and Applications. 2d ed. Boca Raton, Fla.: CRC Press, 2008. Sullivan, Patrick J., Franklin J. Agardy, and James J. J. Clark. The Environmental Science of Drinking Water. Burlington, Mass.: Elsevier Butterworth-Heine- mann, 2005. Thomas, Sarah V., ed. Water Pollution Issues and Devel- opments. New York: Nova Science, 2008. Viessman, Warren, et al. Water Supply and Pollution Control. 8th ed. Upper Saddle River, N.J.: Pearson/ Prentice Hall, 2009. Vigil, Kenneth M. Clean Water: An Introduction to Water Quality and Water Pollution Control. 2d ed. Corvallis: Oregon State University Press, 2003. Web Site U.S. Environmental Protection Agency Water Pollution http://www.epa.gov/ebtpages/ watewaterpollution.html See also: Clean Water Act; Environmental biotech- nology; Environmental degradation, resource exploi- tation and; Environmental law in the United States; Environmental Protection Agency; Hydrology and the hydrologic cycle;Incinerationof wastes; Landfills; Mining wastes and mine reclamation; Oil spills; Popu- lation growth; Water. Water power. See Geothermal and hydrothermal energy; Hydroenergy Water rights Categories: Laws and conventions; social, economic, and political issues Water rights are legal entitlements to use, develop, transfer, and derivebenefits from water resources. They Global Resources Water rights • 1315 . impact on the quality and quantity of water resourcesfor all uses,numerical estimatesof the Global Resources Water • 1309 U.S. Water Use Per Day (billions of gallons) Year Total Per Capita (gallons). epidemics of diseases spread by water, such as cholera, hepatitis, and typhoidfever.The RiversandHarbors Actof1899 prohibited the dumping of trash into bodies of water. In the latter part of the. middle of a large continent. The high heatcapacity of water is closelyassociated with some other unusual properties of water, namely, the latent heat of fusion and vaporization. The latent heat of