Nitrate in community water systems

What is nitrate and how does it get in drinking water?

Nitrate is a substance that occurs naturally in air, soil, water, and plants. Nitrate dissolves easily in water and can be a result of runoff or leakage from fertilized soil, wastewater, landfills, animal feedlots, septic systems, or urban drainage. High levels of nitrate in drinking water are more likely in farming areas, shallow water sources and geologically vulnerable areas, like places with sandy soil.

Nitrate levels in Minnesota drinking water

The U.S. Environmental Protection Agency (EPA) standard for nitrate in drinking water is 10 milligrams of nitrate (measured as nitrate-nitrogen) per liter of drinking water (mg/L). The Minnesota Department of Health (MDH) uses this standard, the Maximum Contaminant Level, (MCL), set by the EPA to ensure safe drinking water in Minnesota.


Community water systems (CWS) are required to monitor for nitrate in drinking water. If test results indicate nitrate levels are greater than the MCL (10 mg/L), an additional sample is taken to confirm the results. Officials must notify the public, reduce nitrate concentrations, and conduct on-going quarterly nitrate monitoring.


In 2017, 92% of Minnesotans who were served by community water systems had average levels of nitrate at or below normal background levels (0-3 mg/L). Most Minnesotans do not drink water above the MCL (10 mg/L), but some systems are vulnerable to nitrate contamination. Ongoing steps are needed to prevent contamination and keep the public safe.


Mean nitrate levels of Minnesota community water systems

 
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

 
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.


 

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

Population served by community water system mean nitrate concentration, 2017

Nitrate Systems Population served Percent
0 - 3 883 4,265,442 96.8%
3+ - 5 58 58,769 1.3%
5+ - 10 22 82,295 1.9%
10+ - 20   0 0.0%

  

Health effects of nitrates in drinking water

Health standards for exposure to nitrate in drinking water are focused on protecting infants. Short-term exposure to high levels of nitrate can cause illness, including death, for infants. Bottle fed babies 6 months or younger have the greatest risk of developing a serious blood disorder called blue baby syndrome (methemoglobinemia). Methemoglobinemia can affect the body’s ability to carry oxygen and cause skin to turn a bluish color. Other symptoms of methemoglobinemia include low blood pressure, increased heart rate, stomach cramps and vomiting.

What can be done about nitrate in drinking water?

You can find the level of nitrate detected in the system serving where you live by reading the system’s Water Quality Report (also known as a Consumer Confidence Report [CCR]). You can call your public water system to get a paper copy of your CCR, or you may be able to find it online at Find Your Local CCR. You can find the level of nitrate detected in the systems serving places other than where you live by contacting the water system. People served by community water systems can find out the nitrate level in their drinking water by reading the Consumer Confidence Report (also called a Water Quality Report) issued each year by their water system For more information about nitrate in drinking water, see MDH Source Water Protection and Nitrate in Drinking Water.

Nitrate is also a concern in private wells. The only way to know if a private well contains nitrate is to have it tested. Private well users are responsible for testing their well water for nitrate. MDH recommends private well users test their water every other year for nitrate, as nitrate levels fluctuate over time. Contact a Minnesota Department of Health (MDH) accredited laboratory to get a sample container and instructions on how to submit a sample. For more information about nitrate in well water, see Nitrate in Drinking Water. See also Water Testing for Nitrate from the Minnesota Department of Agriculture.


 

 

Last updated November 2018. Updates are made when data become available; not all data are available annually.