Nitrates and Nitrites in Well Water

Nitrate (NO3) and nitrite (NO2) are forms of nitrogen. Nitrogen is essential for plant growth, which is why it is a main ingredient in fertilizers. Small amounts occur naturally in groundwater.

Problems arise when human activities add more nitrogen to the environment than soil can absorb. The excess nitrogen moves down through the ground and can reach the aquifer that supplies your well. (USGS)

In most groundwater, nitrate is the more stable and common form. Nitrite can appear as an intermediate form and has its own health-based limit, but nitrate is what most well owners need to watch.

The main concern with nitrate in drinking water is a condition called methemoglobinemia, sometimes called "blue baby syndrome." Nitrate interferes with the blood's ability to carry oxygen. In severe cases, skin can turn bluish.

Infants under six months are most vulnerable. Their digestive systems convert nitrate to nitrite more readily than older children or adults. Many documented cases involve babies who drank formula mixed with high-nitrate well water. (CDC Archive)

For adults, the health picture is less clear-cut at typical exposure levels. But the infant risk alone makes nitrate one of the most important tests for any household with a private well.

Nitrate contamination is not random. It follows nitrogen use on the land surface.

Fertilizers and Agriculture

Commercial farms, lawns, and gardens all use nitrogen fertilizers. When more nitrogen is applied than plants can use, the excess can leach through soil with rain or irrigation and eventually reach groundwater. (USGS)

Septic Systems

Septic systems release nitrogen as part of normal operation. Well-functioning systems in suitable soil usually do not cause problems. Aging, damaged, or poorly sited systems can contribute nitrate to nearby groundwater. (CDC)

Animal Waste

Livestock operations, feedlots, and manure storage areas can be significant nitrogen sources. (CDC)

Why Two Nearby Wells Can Have Different Levels

Nitrate risk depends on both what happens at the surface and how easily contamination can reach the aquifer. Soil type, depth to groundwater, well construction, and land use all play a role. Your neighbor's results do not predict yours. (USGS)

Public health guidance commonly recommends annual nitrate testing for private wells. (CDC Archive)

Test sooner if:

• You are moving into a home with a private well
• A baby will be drinking formula mixed with your well water
• Someone in your household is pregnant
• Your well is in an agricultural area
• Your area has flooding or heavy rains
• Your well has been repaired or opened
• Your health department reports nitrate issues in your region

If you live in an area with known nitrate concerns, consider testing more than once a year. Nitrate levels can change with seasons and rainfall patterns.

Nitrate testing is straightforward compared to bacteria testing. Samples are less time-sensitive and easier to collect.

Use a Certified Lab

Your local health department can recommend state-certified labs. Many labs offer basic well water panels that include nitrate alongside bacteria and other common tests. (CDC)

Follow Sample Instructions

Labs provide specific bottles and instructions. Some require samples to be kept cold during transport. Follow the directions to get accurate results.

Cost and Turnaround

A nitrate test typically costs $15 to $30 when included in a basic well panel. Results usually come back within 5 to 10 business days.

Understanding your results requires knowing how the lab reports nitrate. There are two common formats, and they produce different numbers for the same amount of contamination.

The EPA Standard

The EPA Maximum Contaminant Level for nitrate in public water systems is: (EPA)

• 10 mg/L nitrate as nitrogen (NO3-N)
• 1 mg/L nitrite as nitrogen (NO2-N)

Private wells are not regulated, but these standards are used as reference points.

Understanding "As Nitrogen" vs "As Nitrate"

This is a common source of confusion:

• NO3-N (nitrate as nitrogen): The format used in the EPA standard. The 10 mg/L limit refers to this format.
• NO3 (nitrate as nitrate): Includes the oxygen atoms in the molecule. The same water would read about 44 mg/L in this format.

Check which format your lab uses. If you are unsure, call and ask. Comparing a result in one format to a standard in another format can lead to wrong conclusions.

What Your Number Means

• Below 5 mg/L (as N): Generally considered low. Continue routine testing.
• 5 to 10 mg/L (as N): Approaching the limit. Consider more frequent testing and identifying possible sources.
• Above 10 mg/L (as N): Exceeds the EPA standard. Take action, especially if infants are present.

If your nitrate level exceeds 10 mg/L as nitrogen, take action, especially if infants, pregnant women, or nursing mothers are in your household.

Step 1: Use Safe Water for Infants Immediately

Do not wait for confirmation. Use bottled water or another safe source for mixing formula. State health departments consistently emphasize this as the first priority. (MN DOH)

Step 2: Do Not Boil the Water

This is critical. Boiling does not remove nitrate. It makes the problem worse by evaporating water while leaving nitrate behind. (EPA)

Step 3: Confirm With a Retest

Like any lab result, it is worth confirming. Collect another sample carefully and send it to the lab.

Step 4: Identify the Source

High nitrate usually points to one of these:

• Agricultural activity nearby
• Septic system problems
• Shallow well construction
• Damaged wellhead allowing surface infiltration

A licensed well contractor can help evaluate your well and suggest improvements. (MN DOH)

Step 5: Choose a Treatment Method

Standard water filters (like pitcher filters with carbon) do not remove nitrate. Treatment options that work include: (CDC)

• Reverse osmosis: Usually installed under the kitchen sink. Effective but wastes some water.
• Distillation: Effective but slower and uses more energy.
• Ion exchange: Can be whole-house or point-of-use. Requires maintenance.

After installing treatment, test your treated water to confirm it is working.

You cannot control regional agriculture, but you can protect your well and track changes over time.

Protect the Wellhead

• Keep the cap secure and in good condition
• Ensure ground slopes away from the well
• Keep fertilizers, chemicals, and waste away from the well area

Maintain Your Septic System

Regular pumping and inspection help prevent septic systems from contributing nitrate to groundwater. Address any drainage or backup issues promptly.

Track Your Results Over Time

Save every lab report. Note any changes in land use, weather events, or well maintenance. Patterns over time are more informative than a single test.

Most certified labs offer nitrate testing as part of basic well water panels. Contact your local health department for recommendations, or use our directory to find testing providers in your area.

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