What are Water Quality Standards?
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Aquatic organisms, such as fish, snails, frogs and insects, live in water for part or all of their lives. To protect human health and aquatic life, states, territories and authorized tribes establish water quality standards.
Water quality standards are provisions of state, territorial, authorized tribal or federal law approved by EPA that describe the desired condition of a waterbody or the level of protection or mandate how the desired condition will be expressed or established for such waters in the future.
These standards form a legal basis for controlling pollution entering the waters of the United States from a variety of sources (e.g., industrial facilities, wastewater treatment plants, and storm sewers).
- Designated Uses of the water body
- Criteria to protect designated uses
- Antidegradation Requirements to protect existing uses and high quality waters
- General Policies to address implementation issues.
Each section below links to chapters in the Water Quality Standards Handbook for more detailed information.
The Water Quality Standards 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.
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 criteria 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 regarding water quality standards implementation, such as mixing zone, variance, and low-flow policies. Such policies are subject to EPA review and approval.