Water Quality

What are the Sources of Water Pollution?

Degradation of the quality of a body of water most often results from pollution, defined here as an undesirable [Page 1016]change in the physical, chemical, or biological state of a system. Sources of pollution can be human-made or natural and are classified as either point sources or nonpoint sources. A point source is one that discharges pollution from specific locations, such as industrial discharge pipes, drainage ditches, and sewer outfalls. Because they are discrete and easily identified, point sources are relatively easy to monitor and regulate.

Nonpoint pollution sources, however, are much more problematic. They are diffuse sources, having no discrete discharge location into a specific body of water; some of them are also intermittent, discharging only after a major precipitation event. Because of this diffuse nature, they are much more difficult to identify. This makes them much more difficult to monitor and regulate. Nonpoint sources include farm fields, golf courses, construction areas, parking lots, and the atmosphere.

How are Water Pollutants Classified?

In general, the lowered quality of water can have two major, often overlapping, effects: (1) disruption in the functioning of a natural ecosystem and (2) health problems for humans. The U.S. Environmental Protection Agency (EPA) has identified eight major categories of water pollutants based, in part, on their effects. The first category, oxygen-demanding wastes, includes materials such as animal manure and plant materials. The most common sources of these are agricultural runoff, food processing, paper manufacturing, and sewage.

Plant nutrients such as nitrates, phosphates, and ammonium are most often from fertilizers and manure used for agricultural purposes, urban use of fertilizers, and sewage. Sediment washed into a body of water as a result of land erosion can also degrade the quality of the water. Although erosion is a naturally occurring process, the rate of erosion can be greatly increased by human activities like construction. Heat, specifically hot water, can also seriously degrade the quality of water bodies into which it is discharged. The source of this hot water is the cooling water from power plants and other industrial facilities.

The remaining four categories of water pollutants can cause health problems for humans as well as disrupting natural ecosystems. The first group, pathogens, includes bacteria, viruses, and parasites. Usually introduced into water from human and animal waste, they have caused numerous outbreaks of serious illness throughout human history. Inorganic chemical pollution is most often the result of industrial discharges, surface runoff from developed areas, and improper disposal of household cleaners. This category includes materials such as salts, acids, caustics, and metal compounds.

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