Nitrate in well water

Best for

Homes with nitrate above 10 mg/L as nitrogen, or rising toward it, who need safe drinking and cooking water at the kitchen tap.

Wrong fit

Families with a baby under six months should use bottled water for formula even with treatment in place. Wells with nitrate far above the limit need the source and the well fixed first.

Tradeoff

An under-sink RO system treats one faucet only and removes a large share of nitrate, not all of it, so very high nitrate can still come through above the limit.

Where nitrate comes from

Nitrate is a form of nitrogen. You cannot see, taste or smell it, so a test is the only way to know. The EPA lists chemical fertilizers, animal waste and human sewage as the main sources, reaching wells through groundwater movement, surface water seepage and runoff. Common sources near a home well:

• A septic system or drain field that is too close or failing.
• Manure from livestock, feedlots or manure spreading.
• Fertilizer on fields, lawns and gardens.

Shallow wells are generally more exposed than deep ones. Minnesota notes that natural nitrate in its groundwater is usually below 1 mg/L (ppm), and that a reading above 3 mg/L suggests human-made sources are reaching the water and the level could rise over time.

Is it a health risk?

Yes, mainly for babies. The EPA standard for nitrate is 10 mg/L measured as nitrogen. The EPA explains that infants below six months who drink water above that level can become seriously ill and, if untreated, may die. The illness is methemoglobinemia, or “blue baby syndrome”: nitrate reduces the blood’s ability to carry oxygen, and symptoms include shortness of breath and bluish skin. The EPA describes it as an acute condition that can develop over a period of days.

Minnesota says bottle-fed babies under six months are at the highest risk, and that people with anemia, heart disease, lung disease, sepsis, G6PD deficiency and some metabolic problems may also be at higher risk. It also notes newer research on possible links between long-term nitrate exposure below the standard and thyroid problems, pregnancy outcomes and some cancers, which is still being studied.

Penn State points out that nitrate can be a marker for other contamination. Water that carries nitrate from a septic system or barnyard can carry bacteria and other chemicals too, so test for coliform bacteria at the same time.

Read the units carefully

Labs report nitrate two ways, and the difference is large:

• Nitrate as nitrogen (NO3-N). The EPA standard is 10 mg/L.
• Nitrate as nitrate (NO3). The same limit is about 45 mg/L. Penn State gives both numbers.

A result of 30 mg/L means very different things depending on which unit is on the report. If the report does not say, call the lab. To compare an NO3 result with the 10 mg/L standard, divide it by about 4.4; to go the other way, multiply a nitrate-nitrogen result by about 4.4.

How to test

Use a state-certified lab. The CDC recommends testing private wells for nitrate at least once a year, along with coliform bacteria, pH and total dissolved solids. Minnesota recommends testing nitrate every year and before anyone becomes pregnant or an infant will use the water. Test again after flooding or well repairs. See how often to test well water.

If your result is X, do Y

Minnesota’s steps above 10 mg/L are clear: get drinking water from a safe source such as bottled water, keep babies under six months off the well water, do not try to boil nitrate out, and find and remove potential sources.

Fix the source first

Penn State and Minnesota both put prevention ahead of treatment, because once nitrate is in the groundwater it is costly to remove. Things to check:

• Septic system. Is the drain field working? Is the tank due for pumping? Is it too close to the well?
• The well itself. Penn State advises that the casing extend at least a foot above ground with a suitable cap, and that surface water be diverted away from the wellhead.
• Fertilizer and manure. Keep storage, mixing and spreading away from the well.
• Well depth. If the well is shallow, a deeper well into a less contaminated aquifer may be a long-term answer.

Blending high- and low-nitrate water reduces the concentration, but Penn State warns blended water still may not be safe for infants.

Treatment options

Nitrate is a health problem from drinking it, so treatment usually targets drinking and cooking water at the kitchen tap. Penn State lists three treatments that remove nitrate, and notes that boiling is not one of them.

Do the math on reverse osmosis before you rely on it. At 83 to 92% rejection, water at 20 mg/L comes out at roughly 1.6 to 3.4 mg/L, well under the limit. Water at 80 mg/L could come out at 6.4 to 13.6 mg/L, which may not be. The higher your nitrate, the more important it is to test the treated water and replace the membrane on schedule.

An under-sink RO system is a reasonable choice for nitrate up to a few times the limit. SpringWell’s MOEN reverse osmosis system is one under-sink option. Its product page lists arsenic, lead, TDS and other contaminants but does not list nitrate, so check the system’s performance data sheet for nitrate results before you buy, and choose a system certified for nitrate reduction where possible. The reverse osmosis guide explains what to look for. Minnesota recommends treatment units certified by NSF, UL or WQA for the contaminant you are treating.

Maintenance

• Replace RO prefilters and membranes on the maker’s schedule.
• Test the treated water after installation and at least once a year.
• Keep testing the raw well water every year; rising nitrate means a source nearby is getting worse.

When to call the health department

Call your state or local health department if nitrate is above 10 mg/L and anyone in the home is pregnant, nursing or under six months old, or if nitrate is rising year to year. If a baby who has been drinking the water seems unwell or bluish, contact a doctor right away. Find your state program under states. Nitrate often appears with other farm-related contaminants, and arsenic is another tap-water problem RO can address; see arsenic in well water.