Nitrate

WTR

10 mg/Lhealth goal = legal limit (nitrate as N)

The one contaminant where the health-based number and the enforceable number are the same.

Emerging evidence

Stasis Home ResearchEvery claim on this page is graded against peer-reviewed health research and linked to its primary source.Updated 2026-06

Nitrate's health goal and legal limit are the same number, 10 mg/L (as nitrogen), because that number is anchored to a settled acute harm: infant methemoglobinemia. So being under the limit carries no extra safety margin, and a separate, still-emerging question about long-term cancer risk below the limit is not yet built into either number.

What it is, and where it comes from

Nitrate is the stable, fully oxidized form of nitrogen in water. It is highly soluble and moves freely with groundwater, so soil does not hold it back. In drinking water it is almost always a signal of surface activity that has leached into an aquifer: nitrogen fertilizer, animal manure and feedlots, septic and sewage discharge, and decaying plant matter all convert to nitrate that percolates down. Because of that, levels track land use and water source. Wells and small systems in farmed or septic-served areas can reach the limit, while homes on imported or treated surface water often see little or none. US limits are written as nitrogen (as N); the same level expressed as the nitrate ion is about 4.4 times larger.

Why it matters

The settled harm is in infants. Ingested nitrate is reduced to nitrite, which oxidizes the iron in hemoglobin so the blood carries less oxygen to tissue. Babies under six months are the sensitive group, and water above the limit can make a baby seriously ill. That single endpoint is why the limit exists and why the health goal sits right on top of it. The emerging question is for everyone else. Nitrite plus certain amines in the acid of the stomach can form N-nitroso compounds, and on that basis the relevant cancer agency calls ingested nitrate under those conditions probably carcinogenic to humans. That long-term association is real in the literature but not yet settled, and it is not reflected in the limit, which is the open part of the story for water that is compliant but not zero.

The California health goal for nitrate is set at the same 10 mg/L (as N) as the legal limit, with its basis listed as hematotoxicity (methemoglobinemia), so being under the limit carries no extra margin the way it does for contaminants whose health goal sits far below the limit.California OEHHA, Nitrate Public Health Goal, 2018 (PHG 10 mg/L as N; basis: hematotoxicity/methemoglobinemia)
Infants under six months who drink water above the limit can become seriously ill from blue-baby syndrome, the methemoglobinemia endpoint that anchors the standard.US EPA, National Primary Drinking Water Regulations (nitrate/nitrite MCLs; blue-baby-syndrome health effects)
Nitrite and certain amines in the acid of the stomach can form N-nitroso compounds, and on that basis ingested nitrate under nitrosation conditions is classified as probably carcinogenic to humans, an association that is not yet reflected in the limit.ATSDR (CDC), ToxFAQs / Toxicological Profile for Nitrate and Nitrite (methemoglobinemia; endogenous N-nitroso formation; IARC probably carcinogenic)
Boiling does not help and makes nitrate worse: it drives off water as steam and concentrates the nitrate left behind.Minnesota Department of Health, Nitrate in Drinking Water (boiling concentrates nitrate; infant fail-safe guidance)

What we grade it against

Where the health research draws the line, versus the legal limit.
Contaminant	Health-based level	Legal limit	Source (health-based)
Nitrate (mg/L as N)	10health goal anchored to infant methemoglobinemia	10federal and CA MCL, identical to the health goal	CA OEHHA Public Health Goal, 2018
Nitrate (as nitrate ion)	45same level, expressed as the nitrate ion	45California MCL written as the nitrate ion	CA OEHHA, 2018
Nitrite (mg/L as N)	1the more directly toxic species; usually far lower in water	1federal MCL and MCLG	US EPA National Primary Drinking Water Regulations

Health-based levels come from peer-reviewed research and government risk scientists working without cost constraints. Legal limits are enforceable compromises. Your report grades to the health column.

What helps

Direct fixes

Reverse osmosis (point-of-use, NSF/ANSI 58)
Reduces nitrate at the kitchen tap. This is the same under-sink unit already used for PFAS and chromium-6, so nitrate folds into that one device rather than adding a product.
Removal is high but not absolute. For a home with a baby under six months, public-health guidance is that the infant should not drink even treated water if nitrate is elevated, in case the system fails; bottled water is the fail-safe for that narrow case.

Bigger retrofits

Nitrate-selective anion exchange
A strong-base, nitrate-selective resin exchanges nitrate off the water. This is the standard utility and whole-house approach, the same resin class used for chromium-6 and perchlorate.
Distillation
Boils the water and leaves the dissolved nitrate salt behind in the vessel. Effective but slow and energy-intensive, so not a default.

Free and behavioral

Activated or catalytic carbon (pitcher or block)
Improves taste and odor by adsorbing organic chemicals and chlorine.
Carbon does NOT remove nitrate. Nitrate is a small dissolved inorganic anion, not the kind of compound carbon adsorbs. A carbon pitcher or block does not cover it.
Boiling
Does the opposite of helping. Boiling drives off water as steam and leaves the nitrate behind more concentrated, so it raises the level rather than lowering it. Never boil for nitrate.

Nitrate is the case where the usual science-versus-regulation gap closes: the health goal and the legal limit are the same number, because that number is pinned to a settled harm in infants. Where a home lands depends on its water source and land use. A private well or a small system in a farmed or septic-served area can sit at or above the limit, while a home on treated surface water often sees little or none, so the move is to read your own water report or well test against the limit rather than assume a default. Under the limit, the acute risk is handled, the long-term cancer question below it is still open, and where a household wants to act, the reverse-osmosis unit it already has for other contaminants covers it. There is no new product to buy and no reason to boil.

Common questions

Why is the health goal the same as the legal limit for nitrate?

Because the limit is anchored to a settled acute harm, infant methemoglobinemia, rather than to a long-range cancer-risk extrapolation. California set the health goal at the same 10 mg/L (as N) the limit uses. For most contaminants the health goal sits far below the limit; nitrate is the exception where they coincide.

My water is under the limit. Is the nitrate in it a problem?

For the acute, well-established harm in infants, being under the limit is the relevant line. The open question is long-term: there is an emerging, not-yet-settled association between nitrate below the limit and cancer through N-nitroso compound formation in the stomach, which is not built into the limit. If you want to act on it, the same under-sink reverse-osmosis unit used for other contaminants reduces nitrate.

Will my carbon pitcher or block filter remove nitrate?

No. Carbon adsorbs organic chemicals and chlorine and improves taste and odor, but it does not remove nitrate, which is a small dissolved inorganic anion. Reverse osmosis or a nitrate-selective anion-exchange resin removes it; carbon does not.

Should I boil water to deal with nitrate?

No, boiling makes it worse. It drives off water as steam and leaves the nitrate behind more concentrated, so the level goes up, not down. Reverse osmosis is the clean point-of-use answer.

Where does nitrate in drinking water come from?

Almost always from surface activity that has leached into groundwater: nitrogen fertilizer, animal manure, septic and sewage discharge, and decaying plant matter. Because it moves freely with groundwater, levels track land use, so wells and small systems in farmed or septic-served areas see the most, and homes on imported or treated surface water often see little or none.