What are Water Quality Standards?
Water quality standards (WQS) are provisions of state, territorial, authorized tribal or federal law approved by EPA that describe the desired condition of a water body and the means by which that condition will be protected or achieved. Water bodies can be used for purposes such as recreation (e.g. swimming and boating), scenic enjoyment, and fishing, and are the home to many aquatic organisms. To protect human health and aquatic life in these waters, states, territories and authorized tribes establish WQS. WQS form a legal basis for controlling pollutants entering the waters of the United States.
Core Components of WQS
Water quality standards consist of three core components. This includes designated uses of a water body, criteria to protect designated uses, and antidegradation requirements to protect existing uses and high quality/high value waters.
Additional Components of WQS
States, territories and authorized tribes also have the choice of including additional components in their water quality standards such as general policies and WQS variances.
The WQS regulation requires states, territories and authorized tribes to specify goals and expectations for how each water body is used. Typical designated uses include:
- Protection and propagation of fish, shellfish and wildlife
- Public drinking water supply
- Agricultural, industrial, navigational and other purposes.
Designated Uses Resources:
States, territories and authorized tribes adopt water quality criteria to protect the designated uses of a water body. Water quality criteria can be numeric (e.g., the maximum pollutant concentration levels permitted in a water body) or narrative (e.g., a criterion that describes the desired conditions of a water body being “free from” certain negative conditions). States, territories and authorized tribes typically adopt both numeric and narrative criteria.
One of the principal objectives of the Clean Water Act is to “maintain the chemical, physical and biological integrity of the Nation's waters.” Antidegradation requirements provide a framework for maintaining and protecting water quality that has already been achieved.
Designated uses and water quality criteria are the primary tools states and authorized tribes use to achieve the objectives and goals of the Clean Water Act, and antidegradation requirements complement these tools by providing a framework for maintaining existing uses, for protecting waters that are of a higher quality than necessary to support the Clean Water Act goals, and for protecting waters identified by states and authorized tribes as Outstanding National Resource Waters (ONRWs).
States, territories and authorized tribes may adopt policies and provisions that generally affect the application and implementation of water quality standards, such as WQS variance policies/procedures, mixing-zone policies, and low-flow policies. Such policies are subject to EPA review and approval.