Nitrates in Well Water: Testing, Infants and the Limit

Fertilizer, septic systems and manure

Nitrate is a form of nitrogen. EPA lists its sources in drinking water as runoff from fertilizer use, leaking septic tanks and sewage, and erosion of natural deposits. Its private-well guidance adds animal waste. So a well near farm fields, livestock or a septic system is the kind to keep an eye on.

Nitrite is a closely related form of nitrogen with its own, lower limit. Lab reports often list them as "nitrate-nitrogen" and "nitrite-nitrogen".

• Nitrate limit (MCL)10 mg/L, measured as nitrogen
• Nitrite limit (MCL)1 mg/L, measured as nitrogen
• How often to testEvery year (EPA and Minnesota Department of Health)
• Can you notice it?No. It has no taste, smell or color

Blue baby syndrome

EPA says high levels of nitrate or nitrite in drinking water can cause methemoglobinemia, also called "blue baby syndrome", where the blood can't carry enough oxygen. Infants below six months who drink water with nitrate above the limit could become seriously ill and, if untreated, may die.

That is why the most important use of a nitrate test is for a household with a baby, or with someone pregnant. The Minnesota Department of Health goes further: it recommends that babies under six months not drink well water that has been treated for nitrate either.

Once a year, every year

EPA's advice for private wells is to test every year for total coliform bacteria, nitrates, total dissolved solids and pH. Nitrate tests are among the cheapest a lab runs: Penn State's lab lists nitrate-nitrogen for $15, and the Wisconsin State Laboratory of Hygiene lists a nitrate test for $35.

Your local health department may offer free or low-cost testing; Wisconsin, for example, says households with pregnant people and young children may qualify for free nitrate testing.

Compare against 10 mg/L as nitrogen

Check how your lab reports nitrate. The federal limit is 10 mg/L measured as nitrogen ("nitrate-N"). Some labs report nitrate as the whole nitrate molecule instead, which gives a number about 4.4 times larger for the same water, so confirm the unit before you compare.

• Read your test resultsEnter your lab numbers to compare them against EPA limits and standards.Read my results →
• Private well water by stateModelled nitrate for your county, from USGS.Pick your state →

• If Nitrate is above 10 mg/L as nitrogenAbove the federal limit for public systems. Don't give the water to a baby, and use another drinking source while you look at treatment.
• If Nitrate is detected but under the limitIt meets the limit. Keep testing every year.
• If Nitrate was not detectedNone was found above the lab's reporting limit in this sample. Test again next year.

What lowers nitrate at home

Vermont's health department lists anion exchange and reverse osmosis as systems that can lower nitrate. EPA's private-well guidance also names distillation among on-site treatments.

Boiling is not a fix. Minnesota and Washington both warn that boiling makes nitrate more concentrated, because the water evaporates and the nitrate stays behind.

After installing a system, test the treated water to make sure it works, and keep testing every year. If nitrate is high, your local health department can help you look for the source, since treatment lowers the nitrate you drink but doesn't stop it reaching the well.

Test, then decide

Order a nitrate test, or ask your lab to add it to your yearly bacteria test. For what a full well test costs, see our guide to well water testing prices. If your well has never been tested for arsenic, add that too.

• How much does well water testing cost?Real 2026 prices from state and university labs.See lab prices →
• Arsenic in well waterThe other well test most homes should run at least once.Read the guide →
• Coliform in well waterWhat a positive bacteria test means and what to do.Read the guide →
• How reverse osmosis worksWhat an RO system removes and what it costs to run.Read the guide →