For many people today in certain regions of the world, insufficient fresh water is a serious and growing problem; Myers (1997) put the number of water-short people at 550 million and suggested that it could grow to 3 billion by 2025. The problem becomes most obvious during periods of drought, when water supplies that are marginally adequate under normal conditions become insufficient to sustain a regional population and necessitate major dislocations and emergency interventions. Contamination is a serious problem in some areas, as is lack of easy access in many others; water piped to one's home is the exception to the rule in much of the developing world (Postel, 1985). According to another estimate, a billion of the world's population lack access to safe water, 1.8 billion do not have adequate sanitation facilities, and over 3 million people die of waterborne and sanitation-related diseases every year (Doyle, 1997).
In recent years, the question of the long-term adequacy of the fresh water supply has become a matter of concern in parts of the world, including areas in the United States—especially the southwest (Doyle, 2001)—that had viewed water as a boundless resource in the past. Projecting the effects on global water resources of a rapidly increasing world population, coupled with those of anticipated climate change, is an inexact science, but investigators acknowledge reasons for concern (Vorosmarty, Green, Salisbury, & Lammers, 2000).
About 70% of the total use of water worldwide goes to agriculture and roughly a quarter goes to industry; residential and other municipal uses account for less than 10% (Postel, 1985). In the United States, agriculture uses almost seven times as much water as do all the nation's city water systems combined (Udall, 1986). Much of the increase in agricultural productivity has been attributed to a greatly increased worldwide use of irrigation during the last few decades (Crossen & Rosenberg, 1989). About 40% of the food grown worldwide uses irrigation (Serageldin, 1995). Some of the water used is returned to the hydrologic system, but not all of it is. In some major agricultural regions, the annual withdrawal of groundwater exceeds the natural recharge rate by large amounts, and this fact would appear to spell trouble for a number of states in the relatively near-term future. Severe water scarcity has been called the biggest threat to future food production (Postel, 2001).
The protection of U.S. groundwater from contamination is a major national concern (Office of Technology Assessment, 1984). The Safe Drinking Water Act of 1974 (PL93-523) requires the Environmental Protection Agency (EPA) to promulgate national standards for drinking water and regulations for enforcing them, and it directs the EPA administrator to arrange for the study of adverse effects on health attributable to contaminants in drinking water. What is known about various types of contaminants (microorganisms, particulate matter, inorganic and organic solutes, and radionuclides) and their effects on human health was reviewed in a report of the National Research Council (1977a), the first in a series of NRC reports relating to the U.S. freshwater supply.
Groundwater becomes contaminated in many ways: agricultural runoff containing pesticides and fertilizers, dumping of sewage into rivers, from salt used for deicing of highways—according to the Salt Institute (1980), the use of salt on the highways increased by a factor of more than 12 between 1950 and 1980—chemical emissions into the atmosphere that return to the earth in precipitation, improperly disposed-of hazardous wastes, and from leachate from municipal dumps (Epstein, Brown, & Pope, 1982; Hibbard, 1986; Smith, Alexander, & Wolman, 1987; Weddle & Garland, 1974). Happily, the concentration of lead in water is believed to have declined significantly in recent years due largely to decreased use of leaded gasoline.
Most of the efforts to clean up the nation's waterways have focused on controlling point sources of pollution, as distinct from nonpoint sources, such as urban and agricultural runoff. The effects of nonpoint sources on water quality are more difficult to determine than those of point sources, but they are assumed to be substantial.
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