Tap Water for 500,000 Minnesotans Contaminated With Elevated Levels of Nitrate

Drinking water for an estimated half a million Minnesotans is drawn from groundwater contaminated with elevated levels of nitrate, a toxic pollutant that is linked to cancer and is especially dangerous for infants, according to an EWG analysis of federal and state test data.

About one in eight Minnesotans served by groundwater-based public water systems consume tap water that, in tests performed over the past 10 years, had at least one detection of nitrate at or above the level the state considers a marker of potentially worsening contamination. Tens of thousands more Minnesotans are drinking from private household wells with elevated nitrate.

Nitrate is a chemical component of fertilizer and manure that can run off of farm fields and seep into groundwater. Our analysis shows that nitrate contamination is far worse in parts of Minnesota where the types of soil and geology make it easier for nitrate in fertilizer and manure to get into groundwater.

To its credit, Minnesota is implementing a Groundwater Protection Rule to reduce nitrate in drinking water. The rule – three years in the making and administered by the Minnesota Department of Agriculture – is a welcome first step that must be implemented quickly and robustly. But EWG’s analysis shows that even full implementation of the new rule may be too little, too late to protect Minnesotans – especially those drinking water from private household wells – from unsafe levels of nitrate.

Nitrate’s Health Effects

Under the federal Clean Water Act, the legal limit for nitrate in drinking water is 10 milligrams per liter, or mg/L.1 This limit was set, in 1962, to guard against so-called blue baby syndrome, a potentially fatal condition that starves infants of oxygen if they ingest too much nitrate.

But newer research indicates that drinking water with 5 mg/L or even lower is associated with higher risks of colorectal cancer and adverse birth outcomes, such as neural tube birth defects. And the Minnesota Department of Health says a level of 3 mg/L indicates that “human-made sources of nitrate have contaminated the water and the level could increase over time.

In June, EWG researchers released a peer-reviewed study that found nitrate pollution of U.S. drinking water at levels far below the legal limit may cause up to 12,594 cases of cancer a year. The article reviewed epidemiological studies of the health effects of nitrate-contaminated drinking water. Recent large-scale studies in Spain and Italy and in Denmark found statistically significant increases in colorectal cancer risk associated with nitrate in drinking water at levels of 0.7 to 2 mg/L.

In 2017, the Environmental Protection Agency began the work needed to review and revise the current legal limit for nitrate. But in April 2019, the agency announced it would no longer consider that re-evaluation a high priority. Drinking water with nitrate levels at or below 10 mg/L meets federal standards, but it is clear that protecting public health requires keeping the contamination level far below the legal limit.

Nitrate in Public Water Systems

Data from the U.S. Environmental Protection Agency show that 472,983 Minnesotans – more than the population of Minneapolis – are served by a total of 727 public water systems that were contaminated with at least 3 mg/L of nitrate. Almost 300,000 people drink from public systems contaminated at or above 5 mg/L, and more than 150,000 from public systems with at least 10 mg/L.

Table 1. Minnesota Public Water Systems With Elevated Levels of Nitrate, 2009-2018

  With at Least 1 test >= 3 mg/L With at Least 1 test >= 5 mg/L With at Least 1 test >= 10 mg/L
System Type Systems People Served Systems People Served Systems People Served
Community 95 405,386 55 258,985 20 146,202
Non-community 632 67,597 358 38,251 104 8,448
All public ground water systems 727 472,983 413 297,236 124 154,650

Source: U.S. EPA Safe Drinking Water Information System, from tests by public water systems.

Many public systems have nitrate tests that are dangerously high. Twenty-two systems serving 4,178 people had nitrate tests at twice the legal limit or more, with two of those systems testing close to 50 mg/L – five times the legal limit.

Public water systems are either community or non-community systems. Community water systems mostly serve residents in cities and towns year-round. There are far more non-community systems, which serve sites like churches and schools with their own source of drinking water, but they serve much smaller populations and usually for only part of the year. Out of the 727 public systems that supply drinking water contaminated with nitrate at or above 3 mg/L, 95 are community systems and 632 are non-community systems.

Nitrate in Private Wells

Tests by the Minnesota Department of Health and Department of Agriculture in the past 10 years show that 7,657 Minnesota households drink from private wells with at least one test at or above 3 mg/L of nitrate. Even if those wells serve just three people each, it means almost 23,000 more Minnesotans are drinking water contaminated with nitrate at or above that level.

Table 2. Private Drinking Water Wells in Minnesota With Elevated Levels of Nitrate, 2009-2018

  At least 1 test at or above 3 mg/L At least 1 test at or above 5 mg/L At least 1 test at or above 10 mg/L
Households with Private wells 7,657 5,825 3,364

Sources: Minnesota Department of Health, Minnesota Department of Agriculture Township Testing Program and Central Sands and Southeast Minnesota Volunteer Nitrate Monitoring Networks.

Of the households that drink from private wells, almost 6,000 wells were contaminated at or above 5 mg/L, and more than 3,000 were contaminated at or above the federal legal limit of 10 mg/L. At least 164 households had private wells that tested at or above twice the legal limit, or 20 mg/L.

Mapping Nitrate Contamination

EWG’s interactive maps show the locations and levels for nitrate in Minnesota’s public water systems and private household wells.

The Minnesota Fertilizer Nitrogen Management Plan, released in 2015 and updated this year, found that the millions of pounds of fertilizers and manure applied to cropland each year are the leading sources of nitrate that can pollute drinking water. More importantly, the report found that without careful management, much of the nitrate remains after crops are harvested and can seep into drinking water.

EWG’s maps confirm that nitrate contamination is far worse in regions of Minnesota where the types of soil and geology make it easier for nitrate in fertilizer and manure to get into groundwater. The area of highest vulnerability makes up almost one-fourth of the state and is home to 2.5 million acres of cropland and 6,287 livestock feedlots.

Almost 90 percent of public water systems with nitrate levels at or above 3 mg/L draw on groundwater in or very near areas considered highly vulnerable to nitrate contamination. About the same percentage of private household wells also draws on groundwater in these highly vulnerable areas. If you live in one of these areas, you are very likely drinking nitrate-contaminated water.

Who Is Affected?

Nitrate contamination of drinking water is a largely rural issue. Eighty-five percent of public water systems with at least one test at or above 5 mg/L served people living in rural Minnesota. Fully 98 percent of townships where at least one test of domestic wells revealed nitrate contamination at or above 5 mg/L were located in rural areas.

About half of the communities and households affected by high nitrate levels are located in areas where household incomes fall below the state median. Of 413 public water systems with at least one test at or above 5 mg/L, 203 are located in U.S. Census block groups where household income is less than the state median. Of 617 townships with at least one private well detection at or above 5 mg/L, 299 are also in areas with household income below the state median.

Groundwater Protection Rule May Be Too Little, Too Late

Minnesota’s Groundwater Protection Rule was finalized in June 2019 and will be implemented starting in 2020. The rule is a welcome first step, but it is likely to fall short. Here’s why:

  • Most troubling is that the new rule is designed to prevent nitrate in community water systems from exceeding the EPA’s legal limit of 10 mg/L – despite the growing evidence that the existing legal limit is not safe. The research cited earlier – that nitrate levels as low as less than 1 mg/L may increase the risk of colorectal cancer – means the target level should be set far lower.
  • The new rule bans the application of nitrogen fertilizer in the fall or on frozen soil in highly vulnerable areas. That will affect about 2.2 million acres of cropland and also applies to about 310,000 crop acres around public wells with high nitrate that are designated for protection. But a 2014 survey by the state agriculture department and USDA found that statewide, 61 percent of fields received more nitrogen fertilizer, and 71 percent more manure nitrogen, than recommended by the University of Minnesota. Even higher proportions of fields in highly vulnerable southeast Minnesota received more nitrogen than recommended. To ensure groundwater is safe to drink, state-of-the-art fertilizer and manure management practices are needed on far more fields in the highly vulnerable areas than is required by the new rule.
  • To improve the way farmers and landowners use and manage fertilizer and manure, the rule relies heavily on their voluntary participation. Mandatory best management practices can be enforced but only in areas to protect community water systems with contamination approaching the legal limit. Provisions in the rule could delay enforcement of mandatory measures for years. EWG has steadfastly supported voluntary programs, but they have proven to be too slow and poorly targeted to succeed at addressing the challenges Minnesota faces to make sure people have safe drinking water.
  • Analysis of the nitrate data shows that private wells are also likely contaminated with pesticides and bacteria. People on well water cannot rely on the monitoring and regulatory oversight their neighbors on public water enjoy. The health department directs public education and outreach initiatives to help private well owners but says that in the end, “private well users are responsible for making sure their water is safe for everyone in the household to drink.” There must be far more frequent and systematic testing of private wells, for more contaminants, and more technical and financial assistance designed to help households make sure their water is safe.
  • Finally, the data show that nitrate contamination of Minnesota groundwater, the focus of this analysis, is a serious problem in highly vulnerable areas. If contamination of surface water were included in this analysis, the state’s nitrate problem would appear even worse.

Reliance on treating drinking water so that it has safe levels of nitrate is an expensive and often ineffective way to protect people. It is more effective to prevent nitrate contamination of drinking water in the first place. What is needed is an aggressive policy and programmatic approach that strategically combines voluntary and mandatory approaches to cleaning up Minnesota’s sources of drinking water.

To see more results of this study, click here.

Special thanks to Soren Rundquist, Director of Geospatial Analysis, and Craig Cox, Senior VP, Agriculture and Resources, for their help in completing this report. This report was produced with the generous support of the McKnight Foundation, the Walton Family Foundation and the Pisces Foundation.


  • 1. One milligram per liter is equal to one part per million, or ppm, a measurement often used for reporting water contamination levels. A part per million is about four drops in a 55-gallon barrel of water. The State of Minnesota measures nitrate contamination in milligrams per liter.
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