State Waterbody: Water Quality Criteria


State water quality criteria (WQC) are the maximum ambient (i.e. in-stream) concentrations of contaminants that cannot be exceeded without putting a water body at risk for a particular use.  Contaminants can be chemical, radiological, or microbiological and states set contaminant limits as numeric (e.g. 140 ppb cyanide) or narrative (e.g. “No toxics in toxic amounts”).

Water quality criteria establish a waterbody’s water quality objectives. WQC are established to achieve specific Designated Uses (See “Designated Uses”) and together form Water Quality Standards (WQS), which is the foundation of the water quality-based controls under the Clean Water Act. The WQS program requires state water agencies to 1) designate appropriate uses (e.g. ship channel, fresh water fishery, primary contact water, source of drinking water) for all waters within their jurisdiction and 2) set WQC to achieve and protect those uses.

Once established, designated uses and water quality criteria provide the basis for further management actions under the CWA such as National Pollutant Discharge Elimination System permits (NPDES), enforcement actions, Total Maximum Daily Loads (TMDLs), and voluntary nonpoint source controls (supported by the Section 319 Program).

When developing criteria for specific contaminants, a state can adopt nationally recommended values called Nationally Recommended Water Quality Criteria (NRWQC), which the EPA has developed for approximately 150 pollutants. States may also adopt other federal benchmarks like Maximum Contaminant Levels for drinking water contaminants, or unique state criteria.

How can I use water quality criteria to protect drinking water sources?

There are many approaches stakeholders can take to help states develop water quality criteria that protect drinking water. States do not recognize some drinking water sources with “Public Water Supply” designated use under the CWA, due in part to lack of information about water system locations (see “Designated Uses”). Stakeholders should encourage state environmental agencies to identify and designate all drinking water sources. This will help states form water quality criteria specific to drinking water.

Many contaminants targeted by the Safe Drinking Water Act are not covered by state water quality criteria under the Clean Water Act and therefore are not regulated upstream of water treatment plants. Encouraging your state environmental agency to set Water Quality Standards (WQS) with criteria for all contaminants of concern will help prevent contaminants from entering your drinking water source and protect public health.

In cases where water quality criteria do not exist or where there are only narrative criteria for a contaminant, encouraging states to develop numeric criteria or numeric translators to narrative criteria will help states better interpret and apply these criteria to drinking water sources.

When approaching states: drinking water databases and national mapping tools like EPA’s Drinking Water Mapping Application to Protect Source Waters (DWMAPS) can be used to identify watersheds critical to drinking water and possible pollution threats. In order to determine contaminants of concern to drinking water, you can use the following resources:

Opportunities for involvement

The CWA requires states to review, revise, and adopt water quality standards every three years in a process called the Triennial Review of Water Quality Standards. Drinking water stakeholders can submit comments and information during state-held Triennial Review processes and during periodic “uses attainability analyses”.  Find more information at your state environmental agency website, found here.

For more information on protecting drinking water through the Clean Water Act, see Opportunities to Protect Drinking Water and Advance Watershed Goals through the Clean Water Act: A Toolkit for State, Interstate, Tribal, and Federal Water Program Managers.