Report shows nitrate levels increasing in drinking water in rural Minnesota

March 9, 2020

Nitrate contamination of drinking water has increased across Minnesota’s farm country according to an analysis from the Environmental Working Group (EWG).

EWG announced in a report published on March 4 it had analyzed data from 115 water utilities that had elevated levels of nitrate between 1995 and 2018 and approximately 63 percent (72 systems) saw increases in nitrate during that time, potentially impacting 218,000 people.

The rate was higher for the community water systems with the worst contamination: 67 percent of the systems with nitrate at or above the federal legal limit of 10 milligrams of nitrate per liter (mg/L) serving about 48,500 Minnesotans showed increased contamination over the study period.

Although nitrate occurs naturally in soil at low levels, a contamination level of 3 mg/L or higher indicates a human cause, according to the Minnesota Department of Health.

The 10 mg/L legal limit for nitrate in drinking water, regulated by the Safe Drinking Water Act, is based on a 1962 U.S. Public Health Service recommendation intended to prevent so-called blue baby syndrome, a potentially fatal condition that starves infants of oxygen.

In 2018, the average level for nitrate in the 72 Minnesota systems that have seen worsening contamination was 4.4 mg/L — a 61 percent jump from 1995’s average of 2.7 mg/L.

Nitrate is a primary chemical component of fertilizer and manure that can run off farm fields and seep into drinking water supplies.

EWG’s new analysis, which includes community water systems that rely on groundwater, surface water, or both, is based on Minnesota Department of Health data. Similar comprehensive data for Minnesota’s hundreds of thousands of private wells is unavailable, but it is likely they have seen a similar increase in nitrate contamination because many draw water from the same sources as the public water systems.

NGWA has published a best suggested practice titled Reducing Problematic Concentrations of Nitrates in Residential Water Well Systems. BSPs are free to members of NGWA.