EPA legal limit
10 ppm
Maximum Contaminant Level
EWG health guideline
0.14 ppm
Science-based, stricter target
Health effects
The acute risk is methaemoglobinaemia (blue baby syndrome) in infants under six months — nitrate reduces the blood's oxygen-carrying capacity at a rate infants cannot recover from as quickly as adults. The EPA's 10 mg/L MCL was set specifically to prevent this. For adults, emerging research links nitrate exposure above approximately 0.5–1 mg/L to elevated colorectal cancer risk, thyroid disruption, and adverse birth outcomes. The EWG health guideline of 0.14 mg/L — 71 times stricter than the federal limit — reflects this cancer-risk research. More than 62 million Americans are served by water systems with nitrate detections at or above 3 mg/L.
Where it comes from
Agricultural fertiliser runoff is the dominant source — particularly in Iowa, Nebraska, Kansas, Indiana, Illinois, and California's Central Valley. Animal feedlot waste, septic systems, and urban stormwater contribute additional nitrate. Nitrate is highly water-soluble and mobile — it travels easily into groundwater and does not bind to soil. Private well users in agricultural areas are at particularly high risk; wells are unregulated by EPA and not covered by SDWIS monitoring.
How it's regulated
EPA MCL: 10 mg/L — set in 1992 to prevent acute infant illness, unchanged since. EWG health guideline: 0.14 mg/L, derived from cancer risk modelling. The gap is 71×. Water meeting the federal limit can still exceed the health-based threshold. EPA is currently under pressure to revise the MCL following mounting epidemiological evidence on cancer risk at sub-MCL concentrations — no revision has been finalised as of May 2026.
The EPA vs EWG gap
The legal limit (10 ppm) is 71× higher than the EWG health guideline (0.14 ppm). Water can be legally compliant while still exceeding the science-based threshold.
How to filter nitrate
Not all filters address nitrate. Look for independently certified filters—NSF International certification means the removal claim has been independently verified.
Nitrate is not removed by water ionization. Reverse osmosis (NSF 58) or ion exchange is required. Standard carbon block filters, pitcher filters, and Brita-type filters do not remove nitrate — this is important to understand for infant formula preparation.
Frequently asked questions
What is nitrate in drinking water?
Nitrate is an inorganic compound containing nitrogen and oxygen. It occurs naturally at low levels but reaches elevated concentrations in water primarily from agricultural fertiliser runoff, animal waste, and septic systems. You cannot taste, smell, or see nitrate in water. It is one of the most commonly detected contaminants in US drinking water, particularly in agricultural states.
Is nitrate in drinking water dangerous?
For most healthy adults, nitrate at concentrations below the EPA MCL (10 mg/L) poses low acute risk. For infants under six months, nitrate above 10 mg/L causes methaemoglobinaemia (blue baby syndrome) — a medical emergency. For adults, research published since 2018 links chronic nitrate exposure above approximately 0.5–1 mg/L to elevated colorectal cancer risk, thyroid disruption, and adverse birth outcomes. The EWG health guideline (0.14 mg/L) reflects this research; the EPA MCL does not yet.
What filter removes nitrate from drinking water?
Reverse osmosis (NSF 58 certified) removes 85–95% of nitrate and is the most practical household option. Anion exchange systems also work. Carbon block filters — including NSF 53 certified filters and all pitcher filters — do not remove nitrate. Boiling concentrates nitrate. Water softeners do not remove nitrate. If nitrate is your concern, RO is the only reliable point-of-use solution.
Does boiling water remove nitrate?
No. Boiling water does not remove nitrate — it concentrates it by reducing water volume through evaporation. Boiling is specifically not recommended as a response to elevated nitrate, particularly for infant formula preparation.
What states have the most nitrate in drinking water?
The highest nitrate detections are concentrated in agricultural states: Iowa, Nebraska, Kansas, Indiana, Illinois, Minnesota, and California's Central Valley. However, a 2026 EWG analysis found nitrate at or above 3 mg/L in water systems across all regions, including large cities — upstream agricultural runoff can reach urban surface water sources miles from the fields. Enter your ZIP to see your utility's specific nitrate level.
Is nitrate in your water?
Enter your ZIP code to see the measured level in your specific utility.