Nitrate in Community Water Systems

There are high levels of nitrate in some MN groundwater

Nitrate occurs naturally in air, soil, water, and plants. High nitrate levels in groundwater are often caused by fertilizers, run-off from barnyards or feedlots, septic systems, and decaying plant debris. Higher levels are more likely to be in agricultural areas, shallow aquifers, and geologically vulnerable areas, like places with sandy soil.

Nitrate disrupts the body's ability to process oxygen. Studies show that very high levels increase risk for cancer, birth defects, and miscarriages. Pregnant women, people with heart or lung diseases, and infants are more susceptible.

Some systems have nitrate above the MCL

The Maximum Contaminant Level (MCL) for nitrate is 10 milligrams per liter of water (mg/L). If infants under 6 months old drink water or formula made with water that has more than 10 mg/L of nitrate, they can develop a life-threatening blood disorder called blue baby syndrome.

All community water systems (CWS's) are required to monitor for nitrate. If the average of an initial and a follow-up water sample is greater than the MCL, the water system must notify the public, conduct quarterly nitrate monitoring, and reduce nitrate concentrations.


Mean nitrate levels of Minnesota Community Water Systems

Percent of tested systems, by mean nitrate concentration
The MCL is 10 mg/L. Concentrations are the mean annual levels for community water systems in Minnesota.
The MCL is 10 mg/L. Concentrations are the mean annual levels for community water systems in Minnesota.

In Minnesota, there are a few systems with nitrate at levels of concern. The number of systems in actual violation of the MCL is not equivalent to the number of systems listed in the chart with concentrations above 10 mg/L, because compliance is based on the average of an original sample result and a confirmation sample rather than a system-wide calendar year average.


Maximum nitrate levels of Minnesota Community Water Systems

Percent of tested systems by maximum nitrate concentration
The MCL is 10 mg/L. Concentrations are the maximum annual levels for community water systems in Minnesota.
The MCL is 10 mg/L. Concentrations are the maximum annual levels for community water systems in Minnesota.

The chart above shows the percent of systems by annual maximum concentration. A system may have a number of different wells and treatment processes which result in entry points to the distribution system with different nitrate levels. In this case, the maximum value reflects the highest concentration in any single sample from any entry point, prior to any blending of water. The level of nitrate in blended water that ultimately reaches the consumer's tap may be lower because of dilution from other entry points with lower levels of nitrate.


Most drink water with nitrate below the MCL

Nearly 4.3 million people were estimated to be served by tested systems in Minnesota in 2014. Only 3% of the population served by systems was exposed to average levels of nitrate at or above 3 mg/L. 

However, some systems are vulnerable to nitrate contamination. A small percentage of Minnesotans rely on this water, so ongoing steps are needed to prevent contamination.

Note that the estimates of the number of people served by each system are rough calculations periodically updated by water system managers.

Population Served

Number of people served, by mean nitrate concentration of Community Water Systems, 2015
Nitrate Systems Population served Percent
0 - 3 883 4,213,081 91.9%
3+ - 5 61 98,918 6.3%
5+ - 10 17 29,669 1.8%
10+ 0 0 0.0%

What can be done about nitrate in drinking water?

People served by community water systems can find out the nitrate level in their drinking water by reading the Consumer Confidence Report issued each year by their water utility. For more information about nitrate in drinking water, see MDH Source Water Protection and Nitrate Probability Reports.

Nitrate is also a concern in private wells. For well owners, the only way to know if a well contains nitrate is to have it tested. Water testing services are available from both county health agencies and private laboratories. Well water should be tested annually, as nitrate levels fluctuate over time. To ensure that a laboratory is certified by MDH to test drinking water for nitrate, see How to Search for Accredited Laboratories. For more information about nitrate in well water, see Nitrate in Well Water and Nitrate in Drinking Water. See also Water Testing for Nitrate from the Minnesota Department of Agriculture.