Water Quality Standards

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Water quality standards

The development of water quality standards is a process first mandated by the Water Quality Act of 1965 and continued by requirements in the Federal Water Pollution Control Act of 1972 (PL 92-500), with amendments in 1977, 1982, and 1987 (collectively referred to as the Clean Water Act ). The process is used to establish standards for stream water quality by taking into account the use and value of a stream for public water supplies, propagation of fish and wildlife , recreational purposes, as well as agricultural, industrial, and other legitimate uses. Water quality standards are enforceable by law and are applicable to all navigable waters. The goals of water quality standards are to protect public health and the environment , and to maintain a standard of water quality consistent with its designated uses. Water quality standards provide the "teeth" for water quality legislation and also the yardstick by which performance may be evaluated.

To establish water quality standards for a water body, officials (1) determine the designated beneficial water use; (2) adopt suitable water quality criteria to protect and maintain that use; and (3) develop a plan for implementing and enforcing the water quality criteria. Both uses and criteria constitute water quality standards, and water quality is evaluated based on how well the designated uses are supported.

Appropriate water use is designated by analyzing the existing use of the water as well as the potential to attain other uses based on an assessment of the physical, chemical, biological, and hydrological characteristics of the water and the economic cost and impact of achieving particular uses. The Clean Water Act requires that, whenever possible, water quality standards should ensure the protection and propagation of fish, shellfish, and wildlife and should provide for recreation in and on the stream. States have primary responsibility for designating stream segment uses, so stream uses may vary from state to state. However, stream use as designated by one state must not result in the violation of another state's use of the same stream.

Water quality criteria are most often expressed as numeric constituent concentrations or levels, but may be narrative statements if numeric values are not available or known. Each criterion is based on scientific information available concerning the effect of the pollutant on human health, aquatic life, and aesthetics.

Before the passage of the Clean Water Act, water pollution control efforts were considered successful if they achieved water quality standards. However, under the act, the accepted measurements of successful water pollution control is whether the effluent from point sources, specifically Publicly Owned Treatment Works (POTWs), meets technology-based effluent standards. These standards are based on what can be done with available technology rather than what is required to achieve water quality standards.

Water quality standards were retained, however, as part of the overall strategy to control water pollution. Rather than using water quality standards as the highest goal for determining water quality, the state and federal authorities consider water quality control standards to be the lowest acceptable level of water quality. In addition, point sources may be subjected to more stringent requirements than the use of Best Available Control Technology (BAT) if necessary to meet water quality standards. For example, in stream segments that do not meet water quality standards, states can establish a "total maximum daily load" of pollutants that will achieve water quality standards and assign a permissible share to individual dischargers. State water quality programs must also include provisions to prevent degradation of existing water quality when necessary to maintain existing uses and certain high quality waters.

The attainment of water quality standards is also affected by control of pollution from nonpoint sources, such as agricultural practices that result in the addition of sediments, nutrients, pesticides, and other contaminants to water bodies. The 1987 amendments to the Clean Water Act required states to identify water not meeting its standards due to nonpoint source pollution, identify general and specific nonpoint sources causing the problems, and develop management plans for the control of the these sources.

In 1988, state governments compiled a water quality report for the Environmental Protection Agency (EPA). The report indicated that of 519,412 river miles (835,734 km) assessed (out of a total of 1.8 million mi [2.9 million km] in the United States) 10% did not support their designated uses, 20% partially supported their uses, and 70% fully supported their uses. For lakes, of 16,313,962 acres (6,525,585 ha) assessed (out of a total of 39,400,000 acres [15,760,000 ha] in the United States), 10% did not support their designated uses, 17% partially supported their uses, and 74% fully supported their uses.

See also Agricultural pollution; Agricultural runoff; Criteria pollutant; Marine pollution; Thermal pollution

[Judith Sims ]



Abron, L. A., and R. A. Corbitt. "Air and Water Quality Standards." In Standard Handbook of Environmental Engineering, edited by R. A. Corbitt. New York: McGraw-Hill, 1990.


The Universities Council on Water Resources. "The Clean Water Act." Water Resources Update 84. Carbondale, IL: Southern Illinois University, 1991.