The command for fresh water rises incessantly as the world’s population grows. From 1940 to 1990 withdrawals of fresh water from rivers, lakes, reservoirs, and other sources increased fourfold. Of the water consumed in the United States in 1995, 39 percent was used for irrigation, 39 percent was used for electric power generation, and 12 percent was used for other utilities; industry and mining used 7 percent, and the rest was used for agricultural livestock and commercial purposes. Sewage, industrial wastes, and agricultural chemicals such as fertilizers and pesticides are the main causes of water pollution. The U.S. Environmental Protection Agency (EPA) reports that about 37 percent of the country’s lakes and estuaries, and 36 percent of its rivers, are too polluted for basic uses such as fishing or swimming during all or part of the year. In developing nations, more than 95 percent of urban sewage is discharged untreated into rivers and bays, creating a major human health hazard. Water runoff, a nonpoint source of pollution, carries fertilizing chemicals such as phosphates and nitrates from agricultural fields and yards into lakes, streams, and rivers. These combine with the phosphates and nitrates from sewage to speed the growth of algae, a type of plantlike organism. The water body may then become choked with decaying algae, which severely depletes the oxygen supply. This process, called eutrophication, can cause the death of fish and other aquatic life. Agricultural runoff may be to blame for the growth of a toxic form of algae called Pfiesteria piscicida, which was responsible for killing large amounts of fish in bodies of water from the Delaware Bay to the Gulf of Mexico in the late 1990s. Runoff also carries toxic pesticides and urban and industrial wastes into lakes and streams. (Hammer, G., R. Stone)
Erosion, the wearing away of topsoil by wind and rain, also contributes to water pollution.......................
