Nitrates in Drinking Water

Nitrate is a chemical compound made up of nitrogen and oxygen. It's found naturally in foods like spinach, lettuce, beets, and carrots. It can also be found in groundwater, but usually at very low levels. People typically take in only very small amounts of nitrate in their drinking water.

Nitrate levels

Although low levels of nitrate are naturally present in water, higher levels are sometimes found. The Minnesota Department of Health (MDH) has set a standard of 10 milligrams per liter for nitrate in drinking water. Private well owners should use this level as a safety guideline. Any residential well with a nitrate concentration of more than I milligram per liter should be tested annually.

Where nitrate comes from

It is often difficult to pinpoint where the nitrate in drinking water comes from because there are so many possibilities. The source of nitrate and nitrogen may be from runoff or seepage from fertilized soil, municipal or industrial wastewater, landfills, animal feed lots, septic systems, urban drainage, or decaying plant material.

Health concerns

High nitrate levels in drinking water can pose a special risk for infants. When an infant takes in nitrate, it's converted into another compound called nitrite. Nitrite causes the hemoglobin in the blood to change into a substance called methemoglobin. This reduces the ability of the blood to carry oxygen, causing a condition known as methemoglobinemia, or "blue baby syndrome."

When this happens, the skin turns blue -- similar in color to the blood vessels under the skin. Medical treatment should be sought immediately for this condition. Prompt medical attention usually results in a quick recovery. In severe cases, nitrate poisoning can be fatal.

Why are infants more susceptible?

Adults can take in large amounts of nitrate without any harm. Infants are more susceptible partly because their stomach juices are less acidic. That promotes the growth of a certain kind of bacteria which converts the nitrate into nitrite.

Infants under six months of age are the most susceptible. Older children are rarely affected because of developmental changes that occur as they grow. Women who are pregnant already have elevated methemoglobin levels in their blood. That may make them more susceptible to methemoglobinemia after the 30th week of pregnancy.

Precautions

If your water has nitrate levels above I milligram per liter, have it tested yearly. If you are planning to become pregnant, have your water tested. If your water has nitrate levels above 10 milligrams per liter, remember these precautions:

  1. Infants under six months of age shouldn't drink nitrate contaminated water -- either directly or in infant formula. Infants -- and women in the third trimester of pregnancy-should only drink water that is known to be low in nitrate.
  2. Do not boil high-nitrate water before drinking it. Boiling actually increases the level of nitrate because the water boils away and leaves the nitrate behind.
  3. Seek medical attention immediately if your baby's skin takes on a bluish color.

Testing for nitrate

Federal law requires that public water systems be tested for nitrate, but testing is not required for residential wells. If your infant will be drinking water from a private well, you should have an inexpensive test done for nitrate, in addition to the usual test for bacterial contamination. Many private laboratories can test water samples for nitrates. In some Minnesota counties, well owners can make arrangements with their local public health department to have their wells tested.

For more information on the health effects of nitrate in drinking water, see the MDH web page Nitrate in Well Water or contact us.

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Updated Wednesday, November 21, 2012 at 10:07AM