Contaminant guide

Nitrate in drinking water

Nitrate is one of the most common well-water contaminants in farming regions — and one of the few with an acute health concern, especially for infants. It is also one a carbon filter will not touch, which makes choosing the right treatment type matter.

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A corn field — nitrate in drinking water most often comes from agricultural fertilizer and manure leaching into groundwater.

What it is

Nitrate is a nitrogen-and-oxygen compound that dissolves readily in water. It is naturally present at low levels, but elevated nitrate in drinking water almost always signals human sources nearby — fertilizer, manure, or septic systems. Closely related nitrite is regulated alongside it. Nitrate is colorless, odorless, and tasteless, so it can only be confirmed by a test.

Health effects, stated plainly

Unlike most contaminants here, nitrate's primary concern is acute rather than only long-term. High nitrate can interfere with the blood's ability to carry oxygen, a condition called methemoglobinemia or “blue-baby syndrome,” which is especially dangerous for infants under six months and during pregnancy. For most healthy adults the short-term risk is lower, but the infant risk is the reason the limit exists. The CDC provides a primary-source overview. CDC on nitrate & water →

Nitrate reference level in milligrams per liter A scale from 0 to 20 milligrams per liter as nitrogen. The EPA Maximum Contaminant Level for nitrate is 10 milligrams per liter. 0 10 20 Nitrate as nitrogen (mg/L) EPA limit — 10 mg/L
As of June 2026, the EPA enforceable limit (MCL) for nitrate is 10 mg/L (as nitrogen); for nitrite it is 1 mg/L. Source: U.S. EPA. A health reference, not a treatment mandate.

Where it comes from

The dominant sources are agricultural — nitrogen fertilizer and animal manure that leach into groundwater — along with septic systems. That makes private wells in farming areas the highest-attention case, and nitrate can spike seasonally after fertilizing or heavy rain. Because it moves with groundwater, levels can change over the year.

How to know if you have it

Nitrate is invisible and tasteless, so a laboratory test is the only reliable check — and because levels fluctuate, wells in agricultural areas benefit from testing more than once a year. The CDC recommends private-well owners test for nitrate at least annually.

Start here: a certified lab test, repeated seasonally if you're on a well in farm country. How to test your water →

What the current limit is

As of June 2026, the U.S. EPA enforceable limit (MCL) for nitrate is 10 mg/L (measured as nitrogen), and for nitrite is 1 mg/L. This standard, set to protect against blue-baby syndrome, has been stable for decades and applies to public water systems — private-well owners use it as a health reference. EPA Chemical Contaminant Rules (verified June 2026) →

What reduces it

This is the important part: carbon filters do not remove nitrate. The treatment types that do are reverse osmosis, anion-exchange (a nitrate-specific resin), and distillation. For a household, a certified reverse-osmosis unit at the kitchen tap is the usual route, since nitrate is an ingestion-route contaminant you treat where you drink and cook.

Don't be misled: a whole-house carbon system marketed for “clean water” does nothing for nitrate. Match the treatment type to the contaminant — see how reverse osmosis works.

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Educational information, not medical or regulatory advice. Regulatory limits are health references, not mandates to treat. For your specific water, consult a certified laboratory and your local utility, and confirm any product's current certification for your exact model in the NSF, IAPMO, or WQA database. Regulatory figures verified against the U.S. EPA in June 2026 and may change.