Nitrate in well water: safe levels, who is at risk and what to do

Nitrate is one of the tests every well owner is told to run each year⁵. Low levels occur naturally. High levels usually point to something people have put on or in the ground: fertilizer and manure on fields, lawn fertilizer, or a septic system³.

Penn State cites World Health Organization and National Academy of Sciences findings that nitrate in drinking water is not a significant risk for healthy adults³. For a baby on formula it can be, which is why the limit is set where it is.

The number: 10 mg/L as nitrogen

EPA’s limit for public water systems is 10 mg/L of nitrate, measured as nitrogen². Nobody enforces it on a private well, but Penn State Extension advises well owners to hold their own water to it³.

Labs report nitrate in two different ways, and mixing them up is the most common mistake people make with these results. Penn State gives the limit both ways³:

Your report says	The limit is
Nitrate-nitrogen, nitrate as N, NO3-N	10 mg/L
Nitrate, NO3	45 mg/L

Limits from Penn State Extension, Nitrates in Drinking Water. Labs word the first form in several ways.

Milligrams per liter (mg/L) and parts per million (ppm) are the same thing¹. Our result checker handles both ways of reporting.

Reading your result

Result	What it suggests
Under 1 mg/L	Low. Keep testing every year
1 to 3 mg/L	Still in the range natural processes usually produce. Minnesota suggests considering further testing above 1 mg/L, because pesticides may also be present
3 to 10 mg/L	Under the limit, but more than natural processes usually produce, so a source nearby is probably adding nitrate. Test every year and watch the trend
Over 10 mg/L	Over the limit. Follow the steps below

Our summary of Minnesota Department of Health and EPA guidance.

Minnesota’s health department is the source for both markers: natural processes usually produce less than 3 mg/L, and above 1 mg/L more testing may be wise¹.

Who is at risk

• Babies under six months, especially on formula. Too much nitrate affects how blood carries oxygen and can cause methemoglobinemia, or “blue baby syndrome”, which can cause serious illness or death¹. Lips and skin may turn bluish, but Minnesota warns this can be hard to see in an infant¹. The limit exists to protect this group¹².
• Pregnancy. Wisconsin’s health department says nitrate can raise the risk of neural tube defects in early pregnancy, sometimes before a person knows they are pregnant⁴.
• People with certain metabolic conditions, such as glucose-6-phosphate-dehydrogenase deficiency, may be at higher risk¹.
• Everyone else, over the long term. Some recent research links long-term exposure, even below the standard, with thyroid problems and colorectal and other cancers. Minnesota says more research is needed¹.

If your result is over 10 mg/L

1. Switch drinking water now for the people at risk. Babies, and anyone who is or may be pregnant, should use another source for drinking and for formula⁴. Bottled water is the usual stopgap¹.
2. Don’t boil it. Boiling does not remove nitrate and makes it more concentrated¹.
3. Retest to confirm. If nitrate is still high after retesting, Wisconsin advises that everyone in the house use another source for drinking and for preparing food⁴.
4. Watch the cooking. Use other water for foods that absorb a lot of it, such as rice and oatmeal⁴.
5. Keep bathing and washing as normal. It is fine to use the water for bathing and washing dishes⁴.
6. Have the well inspected. Minnesota recommends a licensed well contractor check it for damage¹.

If nitrate is present, Penn State also suggests testing for other contaminants, such as pesticides, which can be more harmful³.

Find the source before you buy equipment

Minnesota’s advice is to consider home treatment only after you have reduced the sources and confirmed the well is sound¹. Otherwise you are filtering a problem that may keep growing.

• The well itself. The casing should stand at least a foot above the ground and have a proper cap, and surface runoff should drain away from it³. Shallow wells, dug wells and wells with damaged casings are the most vulnerable¹.
• Your septic system. Check that the drain field is working properly; pumping the tank or replacing the field may be part of the answer³. A high nitrate result is one of the listed signs of septic system failure, though a water test alone can’t confirm it⁶.
• Fertilizer and animal waste on your own land. Keep them away from the well¹.
• Farming around you. Here you may have no control over the source³. If the well is too shallow, Penn State says a new, deeper well into a less contaminated aquifer may be the only fix³.

Treatment that works on nitrate

Penn State describes three methods and is frank about their drawbacks³.

Method	What to know
Reverse osmosis	Removes about 83 to 92% of nitrate, so treated water can still be over the limit when the starting level is very high. Slow, and wastes water
Distillation	Very slow, about a gallon every four to five hours, and uses a lot of energy
Ion exchange	Costly and needs maintenance. Works less well with high sulfate, and a saturated resin can release nitrate back into the water

Source: Penn State Extension, Nitrates in Drinking Water.

Do the arithmetic before buying a reverse osmosis unit. At 90% removal, water at 30 mg/L comes out at about 3 mg/L. At 83% removal, water at 70 mg/L comes out at about 12, still over the limit.

For the people at risk, Penn State points out that bottled water for drinking and cooking is a low-cost way to cut the risk while you work on the cause³.

When to test

• Every year. CDC and Minnesota both say to test for nitrate annually⁵¹.
• Before a baby comes home, and when someone in the house becomes pregnant¹⁵.
• After flooding, or after repairs to the well or plumbing⁵.
• If the water’s taste, color or smell changes⁴.

Use a certified or accredited lab¹. Our well water testing guide explains how to find one and what it costs, and the planner below builds a test list for your situation.

Well water test planner Tick what applies to your home and get the tests public health agencies suggest, and why.