Nitrate in community water systems

• Mean nitrate levels
• Maximum nitrate levels
• People served, by mean nitrate level
• Health effects of nitrate in drinking water

What is nitrate and how does it get in water?

Nitrate is a compound that naturally occurs and has many human-made sources. Natural processes can cause low levels of nitrate in drinking water—usually less than 3 mg/L. High levels of nitrate in water can be a result of runoff or leakage from fertilized soil, wastewater, landfills, animal feedlots, septic systems, or urban drainage. It can be difficult to pinpoint where the nitrate in drinking water comes from because there are many possibilities.

Health effects of nitrate

Consuming too much nitrate can affect how blood carries oxygen and can cause methemoglobinemia (also known as blue baby syndrome). Bottle-fed babies under six months old are at the highest risk of getting methemoglobinemia. Methemoglobinemia can cause skin to turn a bluish color and can result in serious illness or death. Other symptoms connected to methemoglobinemia include decreased blood pressure, increased heart rate, headaches, stomach cramps, and vomiting.

The following conditions may also put people at higher risk of developing nitrate-induced methemoglobinemia: anemia, cardiovascular disease, lung disease, sepsis, glucose-6-phosphate-dehydrogenase deficiency, and other metabolic problems.

Only recently has scientific evidence emerged to assess the health impacts of drinking water with high nitrate on adults. A growing body of literature indicates potential associations between nitrate/nitrite exposure and other health effects such as increased heart rate, nausea, headaches, and abdominal cramps. Some studies also suggest an increased risk of cancer, especially gastric cancer, associated with dietary nitrate/nitrite exposure, but there is not yet scientific consensus on this question.

To learn more about nitrate and methemoglobinemia, you can view or download our information sheet Nitrate and Methemoglobinemia (PDF).

Standard for nitrate in community water systems

All community water systems test for nitrate and ensure levels meet the Environmental Protection Agency drinking water standard, or Maximum Contaminant Level (MCL). The MCL for nitrate is 10 milligrams of nitrate (measured as nitrogen) per liter of drinking water (mg/L). Drinking water with levels of nitrate at or below 10 mg/L is considered safe for everyone. 

Nitrate in Minnesota’s community water systems

Nitrate has been detected in surface water and groundwater in many places in Minnesota. Both land use and hydrogeology affect the levels of nitrate in water. Community public water systems with elevated nitrate levels (above 3 mg/L) tend to be in southwestern, southeastern, central, and north-central areas of the state.

In 2022, 93% 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 served by community water systems 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.

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.

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.

What can be done about nitrate in drinking water?

All community water systems test for nitrate and ensure levels meet the EPA standard. If a system’s nitrate level exceeds the standard, the system notifies customers and makes changes to reduce the level.

You can find the level of nitrate your community water system detected by reading their Water Quality Report (also known as a Consumer Confidence Report [CCR]). Call your community water system to get a copy of your CCR, or find it online at Search for Your Consumer Confidence Report (CCR). If you want to find the level of nitrate for a place besides your home, contact the water system serving that location.

For more information, including how MDH works with systems to prevent and respond to nitrate issues, 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 can change over time. See Well Testing, Results, and Options for information about how to test your well water. For more information about nitrate in well water, see Nitrate in Well Water (PDF).
 

Related topics:
• Nitrate in Drinking Water
• Nitrate in Well Water
• Safe Drinking Water For Your Baby
• Minnesota Department of Agriculture – Dealing with Nitrate in Groundwater

Last updated August 2023. Updates are made when data become available; not all data are available annually.