EPA legal limit
1 ppm
Maximum Contaminant Level
EWG health guideline
0.12 ppm
Science-based, stricter target
Health effects
Nitrite is more directly toxic than nitrate: it reacts with haemoglobin to form methemoglobin, reducing blood oxygen-carrying capacity. Infants under six months are most vulnerable — their digestive systems harbour bacteria that convert ingested nitrate to nitrite, and fetal haemoglobin is more susceptible. Methemoglobinemia (blue baby syndrome) can be life-threatening. Adults rarely develop symptoms at drinking water levels, but the EWG guideline accounts for cumulative exposure across all dietary sources.
Where it comes from
Agricultural runoff, septic system leachate, and sewage discharges — the same sources as nitrate. In chloramine-treated distribution systems, bacterial nitrification can generate nitrite within the pipes. Also appears as an intermediate in the nitrogen cycle wherever nitrogen-rich waste or fertilisers enter the water supply.
How it's regulated
EPA MCL: 1 ppm (as N). The combined nitrate + nitrite MCL is 10 ppm. The EWG health guideline of 0.12 ppm reflects cumulative dietary nitrite exposure. Rarely exceeds the EPA MCL in regulated public water systems.
The EPA vs EWG gap
The legal limit (1 ppm) is 8× higher than the EWG health guideline (0.12 ppm). Water can be legally compliant while still exceeding the science-based threshold.
How to filter nitrite
Not all filters address nitrite. Look for independently certified filters — NSF International certification means the removal claim has been independently verified.
Nitrite is not removed by water ionization. Reverse osmosis or ion exchange is the correct solution — especially important for infant formula preparation.
Frequently asked questions
What is nitrite?
Nitrite is closely related to nitrate — it is the reduced form of nitrate and is itself oxidised to nitrate in water. Nitrite exposure in drinking water most commonly comes from agricultural runoff, sewage leakage, or from conversion of nitrate by bacterial activity in low-oxygen plumbing. In water treatment, nitrite is also an intermediate in the nitrification of chloramine-disinfected systems.
What are the health effects of nitrite?
Nitrite is more directly toxic than nitrate: it reacts with haemoglobin to form methemoglobin, reducing blood oxygen-carrying capacity. Infants under six months are most vulnerable — their digestive systems harbour bacteria that convert ingested nitrate to nitrite, and fetal haemoglobin is more susceptible. Methemoglobinemia (blue baby syndrome) can be life-threatening. Adults rarely develop symptoms at drinking water levels, but the EWG guideline accounts for cumulative exposure across all dietary sources.
Is nitrite regulated in drinking water?
EPA MCL: 1 ppm (as N). The combined nitrate + nitrite MCL is 10 ppm. The EWG health guideline of 0.12 ppm reflects cumulative dietary nitrite exposure. Rarely exceeds the EPA MCL in regulated public water systems.
Where does nitrite come from?
Agricultural runoff, septic system leachate, and sewage discharges — the same sources as nitrate. In chloramine-treated distribution systems, bacterial nitrification can generate nitrite within the pipes. Also appears as an intermediate in the nitrogen cycle wherever nitrogen-rich waste or fertilisers enter the water supply.
How do I remove nitrite from tap water?
The most effective methods for removing nitrite are: Reverse osmosis (RO), NSF 58 certified RO system, Ion exchange resin, Distillation. Look for NSF-certified systems — independent certification confirms removal claims have been verified.
Is nitrite in your water?
Enter your ZIP code to see the measured level in your specific utility.