Water quality is a general term to describe the purity of water, usually in a natural setting. Water that contains low concentrations of impurities or pollutants is generally said to be of high quality; water with many impurities or high concentrations of impurities is considered to be of low quality. Evaluation of water quality most often considers its suitability for a particular use. As a result, a body of water may be considered high quality for an industrial application, yet at the same time, be of too low a quality to serve as a drinking water source.
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 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.
In industrial societies, organic compounds are a major source of pollution to natural waters and are probably the single group with which people are most familiar. They can be discharged industrial and household sources as well as released as a result of agricultural use. This very large group includes pesticides, plastics, detergents, and petroleum products (oils, gasoline). Radioactive materials such as radon, iodine, cesium, and uranium can be discharged from a number of sources, including ore mining and processing, power plants, and natural sources.
How Is Water Quality Regulated?
At the federal level, water quality is regulated by the Clean Water Act and by the Safe Drinking Water Act. The Clean Water Act and its amendments regulate discharges from point sources through an enforceable permit system. The National Pollutant Discharge Elimination System (NPDES) established a way to control and eventually eliminate discharges of pollutants from point sources into U.S. surface waters. In many states, the state agency has taken over the day-to-day administration of the NPDES program, but EPA retains oversight authority and maintains the database of submitted water quality data. Nonpoint sources remain unregulated.
The Safe Drinking Water Act was passed to protect public water systems from chemical, physical, and biological contaminants. It does not address discharges but rather regulates the quality of the water provided by public water systems, defined as at least 15 connections, or greater than or equal to 25 people, or one that supplies water for more than 60 days per year. The development of drinking water standards is an ongoing project at EPA.
What Are the Effects on Humans from Decreased Water Quality?
A reliable source of high-quality water is a basic human need. When that source is destroyed or compromised in some way, the results can be devastating to individuals and to society as a whole. Perhaps the best-known recent U.S. example is Love Canal in upstate New York. The canal, originally built in the 1890s, was used during the 1940s and 1950s to dispose of tons of hazardous chemicals. After the landfill was closed, the area was covered over and the property sold and developed. By the 1970s, many homes were having problems with chemical odors and residues in the basements. More importantly, residents reported high incidents of miscarriages, birth defects, and chronic illnesses. In 1978, the New York State Department of Health evacuated residents in the area. Several hundred homes were demolished and cleanup activities begun. Although the area is now considered safe, few of the original residents have returned there. Because many of the chemicals found at Love Canal are carcinogens, many former residents live in fear of long-term health effects, even today.
- Beck, Eckardt C. 1979. “The Love Canal Tragedy.” EPA Journal. Retrieved March 27, 2017 (https://archive.epa.gov/epa/aboutepa/love-canal-tragedy.html).
- Gibbs, Lois Marie. 1998. “Learning from Love Canal: A 20th Anniversary Retrospective.” Orion Afield (Spring). Retrieved March 27, 2017 (http://www.soc.iastate.edu/sapp/LoveCanal.pdf).
- S. Environmental Protection Agency. (https://www.epa.gov/).
- S. Geological Survey, Office of Water Quality. (https://water.usgs.gov/owq/).
- Vigil, Kenneth. 2003. Clean Water: An Introduction to Water Quality and Water Pollution Control. Corvallis, OR: Oregon State University Press.
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