At Risk Drinking Water Sources

At Risk Drinking Water Sources

Americans get their drinking water from one of two places: groundwater (e.g., aquifers), or surface waters. Approximately 10% of people in the United States rely on private wells for their drinking water; the remaining 90% get their water for drinking, cooking, and bathing from public drinking water systems.


Both ground and surface water quality and quantity are protected by intermittent, ephemeral, and headwater streams and their associated wetlands. These streams play a crucial role in ensuring a continuous flow of water to downstream freshwater ecosystems. Specifically, water in streams moves between and among the soil, streams, and groundwater. If these small streams and associated wetlands are filled, downstream waters will be adversely impacted and can even cause some wells to run dry.

These small streams not only protect the quantity of water downstream, but also water quality. Intermittent, ephemeral, and headwater streams trap sediment, and absorb and convert excess nutrients. Bacteria and fungi on the bottom of streambeds converts inorganic nitrogen and phosphorous into less harmful compounds. If these streams are filled, contaminated, or degraded, it can lead to contamination and eutrophication of downstream waters.

The Trump Administration is attempting to redefine waters of the United States (WOTUS) in such a way that will remove federal jurisdiction from these intermittent, ephemeral, and headwater streams and their associated wetlands. Moreover, they are trying to repeal the 2015 Clean Water Rule which specifically protected streams that protect drinking water. The result of this is that these small streams and wetlands will be able to be filled or destroyed without a permit under the federal Clean Water Act.

The data that EPA scientists used (Read EPA methodological descriptionto create the 2015 Clean Water Rule include an analysis of which small streams impact drinking water around the country. The spreadsheets linked below were used by EPA, and display which public surface drinking water systems are dependent on intermittent, headwater, and ephemeral streams for the 48 contiguous United States.

Approximately 117 million people, or more than one-third of the U.S. population, get some or all of their drinking water from systems that rely in part or in entirety on intermittent, ephemeral or headwater streams.

See state-by-state summary of affected streams and wetlands for the percentage of people in your state dependent on intermittent, ephemeral or headwater streams for drinking water.

Look at county-specific breakdown of impacts to see what percentage of your county is dependent on intermittent, ephemeral, or headwater streams, find the data for your state (states are listed alphabetically). Then find your county (counties are listed alphabetically within each state). If your county is not shown, it means that your drinking water does not come from surface water.

See a Legend and Glossary for linked tables.

Other links of interest:

Totals by state

Executive summary of analysis