The short answer: nitrate is a common well contaminant from fertilizer, manure, and septic systems. For most adults it is not an immediate hazard at typical levels, but for infants under about six months it can cause a serious, sometimes life-threatening condition called methemoglobinemia, or "blue baby syndrome." The EPA limit is 10 milligrams per liter (measured as nitrate-nitrogen), set specifically to protect infants. It has no taste or color, so testing is the only way to know.
Nitrate is unusual among well contaminants because its danger is so age-specific. The same water that is unremarkable for the adults in a household can be genuinely dangerous for a bottle-fed newborn. That is why nitrate is one of the two tests recommended every single year, and why it deserves a fresh test before an infant relies on your well water.
Where nitrate in wells comes from
Unlike arsenic, which is geological, nitrate is mostly a surface and land-use contaminant. It enters groundwater from:
- Agricultural fertilizer and animal manure, which is why nitrate is especially common in wells near cropland and livestock operations.
- Septic systems, particularly older or failing ones, and clusters of septic systems on small lots.
- Natural sources in smaller amounts.
Because it comes from the surface, nitrate is more likely in shallow wells and can vary seasonally, rising after fertilizer application or heavy rain that flushes nitrate down into the water table. This variability is the reason a one-time reading from years ago is not reliable, and why annual testing matters.
Why infants are uniquely at risk
When an infant consumes water high in nitrate, bacteria in the digestive tract can convert nitrate to nitrite. Nitrite interferes with the blood's ability to carry oxygen by converting hemoglobin into a form (methemoglobin) that cannot release oxygen to the body's tissues. The result, methemoglobinemia, can cause a bluish tint to the skin, especially around the lips and extremities, and in severe cases can be life-threatening.
Infants under about six months are far more vulnerable than older children or adults for a few reasons: their digestive systems more readily convert nitrate to nitrite, their fetal-type hemoglobin is more easily affected, and, if formula-fed, they consume a large volume of water relative to body weight. This combination is why the EPA limit is built around protecting infants rather than adults.
Do not boil water to reduce nitrate
Boiling water does not remove nitrate. Because boiling evaporates some water, it actually concentrates nitrate, making the level slightly higher, not lower. If a test shows nitrate above 10 mg/L and there is an infant in the home, use a known-safe alternative water source for preparing formula until the problem is addressed, and follow guidance from your health department or pediatrician.
Why the EPA limit is 10 mg/L
The EPA's Maximum Contaminant Level for nitrate is 10 mg/L measured as nitrate-nitrogen (sometimes written as 45 mg/L when measured as the nitrate ion; make sure you know which your lab reports). This limit was set specifically to protect against infant methemoglobinemia, and it is legally enforceable for public water systems.
As with every EPA limit, a private well is not legally obligated to meet it, but 10 mg/L is the right threshold to act on, because it is the level a public utility must not exceed to keep infants safe. If your well serves, or may soon serve, an infant, the limit is not academic.
How to test for nitrate
- Test at least once a year, and again before an infant relies on the water, since nitrate can change seasonally.
- Use a certified drinking-water lab or your county or state health department, some of which offer free or low-cost nitrate testing for private wells.
- Confirm the units. Ask whether the result is reported "as nitrogen" (limit 10 mg/L) or "as nitrate" (limit about 45 mg/L) so you compare against the right number.
- Retest after heavy rain or nearby fertilizer application if you are near cropland and got a borderline result.
If your nitrate is high
Effective treatment for nitrate includes reverse osmosis, ion exchange, and distillation; standard carbon filters and boiling do not remove it. Because the right approach depends on your water chemistry and how the water is used, confirm the result with a certified lab and consult a water-treatment professional. In the meantime, if an infant is in the home, switch to a safe alternative source for formula.
Sources
- US Environmental Protection Agency. National Primary Drinking Water Regulations. Nitrate MCL of 10 mg/L (as nitrogen), set to protect infants. epa.gov.
- US Centers for Disease Control and Prevention. Nitrate in Drinking Water and Private Well Water. Methemoglobinemia ("blue baby syndrome") in infants and the recommendation to test annually. cdc.gov.
- US Geological Survey. Nitrate in Groundwater and Domestic Wells. Occurrence of nitrate in private wells and its link to agricultural and septic sources. usgs.gov.
Related guides
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