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Nitrates and nitrites are nitrogen-oxygen molecules that occur naturally at low levels in water. Nitrate is most often used as a fertilizer. Nitrate is more commonly found at higher levels than nitrite, particularly in areas where nitrogen-based fertilizers are used. Once taken into the body, nitrates are converted into nitrites. Nitrates are not normally dangerous to human health unless they are reduced to nitrites.

Nitrates and nitrites can enter drinking water from nitrate-containing fertilizers, sewage and septic tanks, and decaying natural material such as human waste, livestock manure, and decaying plants. Nitrate is very soluble in water and moves easily through the soil. Nitrates and nitrites are likely to remain in water until taken up by plants or consumed by other organisms.

Did You Know?
Animal pens and compost piles should be located far away from private wells in an area where runoff from rainwater will not contaminate the well water.

High levels of nitrates in drinking water can cause serious illness and sometimes death. Infants are more prone to the effects of nitrate exposure due to the change of nitrate to nitrite by the body, which can interfere with the oxygen-carrying capacity of the child's blood. This can be an acute condition in which health deteriorates rapidly over a period of days. Symptoms include shortness of breath and blueness of the skin.

Long term exposures to nitrates and nitrites above the drinking water standard, or Maximum Contaminant Level (MCL) have the potential to cause:

  • Frequent urination
  • Increased starchy deposits in the kidneys
  • Hemorrhaging of the spleen

Long term exposures to nitrates may also cause adverse reproductive effects and some cancers, but these associations are inconclusive at this time and health standards are focused on protecting infants.

The MCL for nitrates is 10 mg/L.

Data Considerations

When reviewing and interpreting drinking water nitrate data, it is important to take into consideration the following:

  • The data presented are for public water systems only. Residents may have exposure to nitrates from private well water.
  • Exposure to nitrates in drinking water depends upon the concentration of nitrates in the drinking water and the amount of water consumed by the individual. Water consumption varies by such factors as climate and level of physical activity.
  • Many factors can affect whether exposure can lead to a health problem, including level of contamination, amount of water consumed, and the length of time water was contaminated. Some populations may be more susceptible to health problems following exposure, such as pregnant woman, children, and immune suppressed individuals.
  • This website provides a summary of drinking water violations by community. Consumer Confidence Reports on public drinking water quality are required to be provided annually to consumers. Your Community Water System should be contacted for this report, which will provide more detailed information on any specific water system violations.
  • Community Water Systems (CWSs) can serve areas substantially beyond the boundaries of the principal city/town served.
  • Multiple CWSs can serve the same city/town and multiple cities/towns can be served by a single.
  • For a list of all Massachusetts Community Water Systems and communities served, click here (pdf).

For additional information, please read the FAQ.

Available Data on Water Quality Measures for Nitrates

Click the Explore Maps & Tables link button on this page to access the following measurse for nitrates in your community. The most current available data will be shown. Be sure to check the site periodically as new data are added each year.

To protect privacy, no information is shown that could identify an individual home or family.

  • Maximum nitrate concentration by number of Community Water Systems and year of testing
  • Mean nitrate concentration by number of Community Water Systems and year of testing
  • Maximum nitrate concentration by number of people served by the Community Water Systems and year of testing
  • Mean nitrate concentration by number of people served by the Community Water Systems and year of testing
  • Mean nitrate concentration by individual Community Water System or county and year of testing
  • Drinking water violations by Community Water System or community and year of violation
More About the Data

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