Sewersheds

EPA’s National Sewershed Dataset

Use Cases

Economic Growth: Identify opportunities for targeted infrastructure investment and expansion of services to unsewered communities.

Public Health: Monitor and predict community health trends as an early warning system through wastewater analysis and knowledge of the affected areas.

Community Awareness: Enable public access to information on where their wastewater goes. This information will also assist utility managers and local government with planning for the future.

Note: This map should not be used as an authoritative source for property-level connections. Sewershed boundaries can change due to growth and changes in inter-governmental agreements. Local governments are typically the most reliable source for determining whether a specific property is served by a centralized wastewater system.

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For questions about this site or the data, please contact us at the CWNS Email Box (CWNS@epa.gov) and include “sewersheds map” in the subject line.

EPA’s Sewershed Boundaries Map

Scope

EPA developed a national dataset of wastewater sewershed boundaries map that includes nearly 17,000 publicly owned wastewater treatment works (POTWs) that cover roughly 78 percent of the U.S. population reported in the 2020 census (according to the 2022 Clean Watersheds Needs Survey, 82 percent of the U.S. population is served by POTWs). The POTWs in the dataset include “endpoint facilities” (meaning they are the last point of treatment before discharging to the environment) and POTWs where less than 50 percent of their wastewater is sent to another facility (meaning the majority of the wastewater receives its final treatment at that facility).

This dataset extends to all 50 states and Washington, D.C. Real sewersheds are used in lieu of modeled sewersheds wherever possible. Approximately 19 percent of the sewershed boundaries are from known sewersheds sourced online or directly from the state or utility. Future updates will aim to improve existing sewershed boundaries and add POTWs that are not currently in the dataset. For more detailed information, see the Sewershed Methods Documentation.

Methods and Attributes

In 2024, EPA released a model estimating drinking water service area boundaries. While similar, wastewater infrastructure requires a distinct model due to differences in system size and cost. The wastewater model uses EPA data sources like the 2022 Clean Watersheds Needs Survey and ICIS-NPDES, combined with census, land use, topography, and other public datasets, to predict service area extents using machine learning. State-provided and online sewershed maps were used to train the model after quality review.

The sewersheds are built using H3 Hexagons, a global grid system of uniformly sized hexagons, facilitating efficient statistical calculations. The model uses level 9 resolution, approximately 0.11 km². For more information on the model development, see the methods documentation and associated Github site.

Limitations

The POTWs’ locations and population served came from a combination of permit records and the 2022 Clean Watersheds Needs Survey results, which were self-reported by state staff during the survey. EPA could not verify data for all modeled POTWs. Some facilities were excluded when technical data proved unreliable (e.g., multiple POTWs using the same address). Privately-owned wastewater treatment facilities are not included in the dataset.

Sewershed boundaries are often changing; towns and cities grow and inter-governmental agreements change. Local government bodies are typically the most accurate source of information to determine whether a particular wastewater system serves a property. Their websites frequently have a “new resident information” page or a general information number. County and regional planning offices will also be able to provide guidance. Sewershed polygons on the map are color-coded to indicate whether the boundary is EPA-modeled or from an external data source.