Water quality standards

The water quality standards for groundwater and surface water help protect — and allow us to regulate the quality of — water in Washington by setting pollution limits. Water quality standards are the backbone of our regulations and describe how clean lakes, rivers, groundwater, and marine waters need to be for the health of people and other species, and to control pollution.

Groundwater quality standards

The goal of the groundwater quality standards is to maintain the highest quality of groundwater by reducing and eliminating groundwater contamination. We work to protect groundwater from pollution so that it's drinkable and meets state standards.

Surface water quality standards

The surface water quality standards are the basis for surface water quality protection in Washington. The standards implement portions of the federal Clean Water Act by specifying the designated uses for water in Washington. We set water quality criteria to protect those uses. We use them as a foundation to keep water clean and healthy. We use them to assess the health of Washington's surface waters and set pollution limits. We set pollution limits in water quality permits based on the standards. Municipalities, industries, and other water dischargers are required to have water quality permits to operate. The standards also contain policies to protect high quality waters and specify how to implement the standards.

Our surface water quality standards have a three-part approach, they cover:

Designated uses

We ensure the state's waters are protected and able to be used by four types of designated uses:

  • Aquatic life
  • Recreation
  • Drinking water supply
  • Miscellaneous uses

Surface water quality criteria

Water quality criteria protect the designated uses. The surface water quality standards contain numeric and narrative criteria for both marine and fresh waters.


Antidegradation helps us prevent unnecessary lowering of water quality, especially in more pristine areas that have good water quality. It provides a framework to identify waters we set as an “outstanding resource" that may recieve extra protections. Our antidegradation standards follow federal regulation guides.