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Introduction to WQS, continued

Designated uses, water quality criteria, and an antidegradation policy and implementation methods constitute the three major components of the Water Quality Standards Program. The designated uses (DUs) of a water body are those uses that states, territories, and authorized tribes determine the water body should be clean enough to fully support, regardless of its current condition. The DUs are the goals set for the water body. In some cases, these uses have already been attained; sometimes conditions in a water body do not support all the DUs.

Water quality criteria (WQC) are numeric and narrative descriptions of the conditions in a water body necessary to support the DUs. These can be expressed as concentrations of pollutants, temperature, pH, turbidity units, toxicity units, or other quantitative measures. WQC can also be narrative statements such as “no toxic chemicals in toxic amounts.”

Antidegradation policies are a component of state/tribal WQS that establish a set of rules that should be followed when addressing proposed activities that could lower the quality of surface waters.