Nitrate in Drinking Water
Nitrate is the contaminant where the age of the person drinking matters most. For adults it is usually low-risk at regulated levels; for young infants it can be life-threatening.
Nitrate is a compound of nitrogen and oxygen that occurs naturally at low levels but reaches concerning concentrations mainly through human activity. It is highly soluble and moves easily through soil into groundwater, which makes it one of the most common contaminants in agricultural regions and in wells near farmland.
What nitrate is
Nitrate itself is colorless, odorless, and tasteless. The number you will see on a water report is usually "nitrate as nitrogen," which is the standard way the limit is expressed. Like arsenic, it gives no sensory warning, so the only way to know your level is to test.
Where it comes from
The main sources are nitrogen fertilizer, animal manure, and septic systems. Rain and irrigation carry nitrate down into aquifers, so shallow wells in farming areas and downstream of feedlots or failing septic systems tend to show the highest levels. Public utilities monitor and treat for nitrate; private wells, again, are on their own.
The health risks
Nitrate’s signature danger is to infants under six months. In a baby’s body, nitrate interferes with the blood’s ability to carry oxygen, causing "blue baby syndrome" (methemoglobinemia), which can be fatal. This is why formula should never be mixed with water that has not been confirmed safe for nitrate. For adults, nitrate at regulated levels is generally low-risk, though ongoing research examines possible links to some cancers and thyroid effects at higher exposures.
The EPA limit
The EPA sets the maximum contaminant level for nitrate (as nitrogen) at 10 milligrams per liter. Unlike many contaminants whose harm is cumulative, nitrate’s most serious effect is acute and aimed at infants, so the limit is set to protect that most vulnerable group. A well above 10 mg/L should not be used to prepare infant formula until it is treated or an alternative source is used.
Testing and removal
Nitrate is part of most standard well-water panels, so a basic lab test will usually include it, as covered in how to test your water and private well water safety. Boiling, carbon filters, and standard softeners do not remove nitrate. The methods that work are reverse osmosis, covered in our reverse osmosis guide, ion exchange designed for nitrate, and distillation. If your well is near agriculture, put nitrate on your regular testing list rather than waiting for a reason to check.