National Nitrate Analysis of Large and Very Large Drinking Water Systems

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About the Map

Locations of ‘large’ and ‘very large’ community water systems with nitrate levels in drinking water detected at or above 5 milligrams per liter between 2017 and 2019


At least one nitrate test at or above 10 mg/L
At least one nitrate test at or above 5 mg/L, no tests at or above 10 mg/L

This map shows the approximate locations of “large” and “very large” community water systems in the U.S. that detected the presence of nitrate at or above 5 milligrams per liter, or mg/L, between 2017 and 2019 at least once.

The federal legal limit for nitrate in public drinking water is 10 mg/L, an outdated and insufficiently protective level.

Community water systems, or public water systems that serve at least 25 people year-round, provide drinking water to cities and towns. Large systems serve between 10,001 and 100,000 people, and very large systems serve more than 100,000 people.

The yellow points on the map represent water systems that detected nitrate at or above 5 mg/L, but did not detect nitrate at or above 10 mg/L. The purple points represent systems that detected nitrate at or above 10 mg/L at least once between 2017 and 2019.

Clicking on a point brings up information about each water system. The water system name; whether it is a large system or a very large system; the population that it serves; whether the system mainly uses groundwater or surface water; and the city and county served by the system are all provided in the pop-up box. Some systems serve multiple cities or serve a small subset of a city only, so the city served for those systems is not reported.

Each system also has a table that shows the total number of nitrate tests conducted by that system between 2017 and 2019, the number of tests that detected nitrate at or above 5 mg/L and the number of tests that detected nitrate at or above 10 mg/L.

We analyzed data for all large or very large systems that have elevated levels of nitrate, that is, at least one test at or above 3 mg/L. That level was chosen to represent “elevated nitrate” because government agencies believe this level indicates human-caused contamination, and that levels may increase over time in drinking water.

The map only displays systems that tested at or above 5 mg/L, because research has shown that at that level, there is strong evidence for a higher risk of health problems such as colorectal cancer, thyroid disease and neural tube birth defects. But health impacts are also associated with exposure to nitrate in drinking water below 5 mg/L.

EWG’s recommended nitrate drinking water standard to protect against cancer and harm to fetal development is 0.14 mg/L, far below the outdated federal limit of 10 mg/L.

Community water systems conduct tests for nitrate, then provide the results to state agencies, usually health or environmental departments.

EWG obtained the water system data by filing public records requests with the state agencies that maintain the drinking water test data. For more information, see the Methodology page in EWG’s Tap Water Database.

Data about water system attributes, including the populations served, is on the Environmental Protection Agency’s Safe Drinking Water Information System website.

Click here to view the report.

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