How Are Water Quality Standards Determined?


Quick Answer

The Clean Water Act requires states or Indian tribes in control of water sources to establish water quality standards for each body of water in their jurisdiction. The Alaska rule requires the state or tribe to submit their standards to the EPA for approval. The Clean Water Act requires states and tribes to adopt the toxic pollutant standards established by the EPA.

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How Are Water Quality Standards Determined?
Credit: U.S. Department of Agriculture CC-BY-2.0

Full Answer

The act requires the governing body to establish a designated use for each body of water. There are different standards required for each designated use. Bodies that supply drinking water have a higher standard than those used for recreation or transportation. In certain cases, the governing body must re-examine the designation every three years.

The EPA gives states some leeway in the standards due to site-specific requirements. However, it maintains the right to accept or decline the modifications the state requests. In all cases, the state must prove any modifications are appropriate using scientific data.

The standards include biological, chemical and physical assessments. The biological assessments include looking at harmful organisms and environmentally sensitive ones. From a chemical standpoint, scientists look for substances that reduce the water quality or are toxic to humans. From the physical standpoint, they consider bends in streams, aquatic life and other factors that affect water quality.

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