Basic Information on Water Quality Criteria
EPA develops criteria for determining when water has become unsafe for people and wildlife using the latest scientific knowledge. These criteria are recommendations. State and tribal governments may use these criteria or use them as guidance in developing their own.
Section 304 (a) (1) of the Clean Water Act (PDF) (6 pp, 153 K, About PDF) directs EPA to develop these criteria.
Aquatic Life Criteria
EPA bases aquatic life criteria on how much of a chemical can be present in surface water before it is likely to harm plant and animal life. EPA designs aquatic life criteria to protect both freshwater and saltwater organisms from short-term and long-term exposure.
Biological criteria are indications of how healthy water bodies based on how many and what kinds of organisms are present.
Human Health Criteria
Pollutants can harm people’s health when they drink water or eat seafood from contaminated surface water. EPA scientists research how much of a specific chemical can be present in surface water before it is likely to harm human health. Based on this research, EPA develops human health criteria.
Bacteria and other pathogens can make our waters unsafe for humans. EPA develops microbial criteria to determine when water is safe for recreational activities such as swimming.