Freshwater makes up less than three percent of earth's water, but is the source of virtually all drinking water. In 2002, each U.S. household used an average of 94,000 gallons of water per year. Some 55 percent of that water comes from reservoirs, rivers, and lakes, and a 2000 survey published in EPA's National Water Quality Inventory found almost 40 percent of U.S. rivers and 45 percent of lakes are polluted. These sources, called surface water, are vulnerable to pollution discharged out of pipes and precipitating out of the air but the primary source of their pollution today is runoff, pollutants washing off the land.
These nonpoint or scattered sources are not easily traceable. Pesticides and fertilizers used in agriculture and on golf courses and suburban lawns account for a major portion of nonpoint source pollution. Runoff from parking lots and roads flush spilled oil and gasoline and road salt into lakes and streams. Runoff containing manure from livestock and poultry producers has
Firemen standing on a bridge over Cuyahoga River to spray water on the burning tug boat Arizona, which caused an oil slick at the Great Lakes Towing Company site, Cleveland, Ohio (November 3, 1952). (©Bettmann/Corbis. Reproduced by permission.)
been a major source of surface water pollution. More than 150 pathogens found in livestock manure pose risks to humans. In 2003, concentrated animal feeding operation guidelines, or CAFO standards, were finalized requiring inspection of waste lagoons and outdoor manure tanks, as well as permits for applying manure on land.
Air pollutants such as dioxin and mercury along with sulfur and nitrogen oxides precipitate into lakes and rivers by rainfall in the form of acid rain. More than 95 percent of rainwater tested at four sites in Indiana between 2001 and 2002 contained unsafe levels of mercury according to a National Wildlife Federation report.
Point sources, such as chemical and municipal wastewater treatment plants, were the leading source of contamination for about ten percent of river and lake water according to the 2000 National Water Quality Inventory. Toxic chemicals, although now regulated, can still be discharged directly into surface water. AK Steel Corporation in Pennsylvania discharged the largest amount of any industrial pollutant, about 28 million pounds of nitrate compounds, to surface water between 1998 and 2000, according to the Toxic Release Inventory.
Other sources of surface water pollution include silt washed into streams and lakes that smothers organisms on the lake floor, upsetting or destroying aquatic ecosystems. Thermal pollution such as an influx of warm water from cooling towers for power plants also has a detrimental effect on aquatic ecosystems.
The recent discovery of surface-water contamination by minute amounts of pharmaceuticals and personal-care products, including synthetic hormones
from birth control pills, is being investigated to determine whether it poses a threat to humans, aquatic species, or wildlife. Water Quality Act amendments of 1987 established a $400-million program to help states to develop and implement nonpoint source management programs based on watershed protection.
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