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This data is included as part of the Environmental Health Disparities Version 3.0 map. To see this map, visit our webpage. For more technical information on this map and the model used, visit our Environmental Health Disparities Map Report Version 3.0.
Background
Water is vital for drinking, aquatic life, agriculture, and recreation. It is also crucial for ecosystems and has cultural significance. This measure assesses the quality of waterbodies, which can affect aquatic life and impact human and animal health. For example, pollutants like dioxins can impact the reproduction and development of both people and fish. People who use well water are more affected by environmental water quality because their water is not treated or regulated like water from municipal systems.
Water quality and health risk vary by location. This puts some communities at greater risk. These communities often have less economic access and more people of color.
Testing water quality is important for the health of humans, animals and aquatic life. Under the federal Clean Water Act, all states must keep a list of polluted waters. In Washington, the Department of Ecology (ECY) assesses waterbodies based on the credible data submitted to the agency. From the data that is submitted, Ecology determines which waters are polluted, which are clean, and which do not have enough data to make a determination. Assessing water quality helps find where water is most impacted by pollutants. This information guides water quality improvement plans.
Evidence
Polluted water is linked to sickness in both humans and animals, aquatic habitat damage, and bad smells [1, 2]. Communities with both less economic access and more of people of color often face more pollution in their waters [3]. Climate extremes, such as droughts, can impact water quality by concentrating pollutants and increasing water temperature. This can affect health and safety [4]. Heavy rain can also wash pollutants into waterways [5].
Data source
Washington State Ecology Water Quality Atlas: Water Quality Atlas - Start Page
Washington State Ecology Water Quality Assessment: Assessment of state waters 303d - Washington State Department of Ecology
Method
This measure displays the total number of unique pollutants in each census tract, based on findings from all water bodies within that tract assessed by ECY as falling under categories 4a, 4b, or 5. This measure is modeled after CalEnviroScreen’s Impaired Water Bodies Measure.
Caveats
This measure is not comprehensive. Areas that do not have the resources for water assessment, or that capture their water quality by different metrics, are not included. This measure should be used as a starting point, and not as a sole basis for funding decisions.
Water quality on Tribal lands is not included. Tribal governments have requested that Ecology not assess Tribal waters as part of the State’s Water Quality Assessment. Some Tribes in Washington have their own Clean Water Act standards. We plan to confer with Tribes about their level of interest in exploring a process for including their data in this measure, and how we might collaborate on other ways Tribes would like water quality to be represented.
This measure represents the entire census tract, not individual areas within it. These data should always be supplemented with local data and equitable engagement for more accurate insights.
Additional Resources
Sources
Citation
Washington Tracking Network, Washington State Department of Health. Web. "Water Quality". Data obtained from the Department of Ecology, 2018 Water Quality Assessment Data. Published September 2025.