The safe limit for nitrite in drinking water is 1 mg/L (one milligram per liter), measured as nitrogen. This is the maximum contaminant level set by the U.S. Environmental Protection Agency and enforced for all public water systems. Expressed differently, that’s equivalent to 3.3 mg of nitrite per liter, or about 3.3 parts per million.
How the Safety Limit Is Set
The EPA’s maximum contaminant level for nitrite is based on preventing a condition called methemoglobinemia, sometimes known as “blue baby syndrome.” Nitrite interferes with hemoglobin’s ability to carry oxygen by changing the iron in red blood cells from a functional form to one that can’t bind oxygen. When too much hemoglobin is affected, tissues don’t get enough oxygen, and in severe cases the skin turns bluish.
The 1 mg/L limit is specifically designed to protect the most vulnerable group: bottle-fed infants under four months old. Babies in this age range are at the highest risk because their stomachs are less acidic, which allows bacteria to convert nitrate into the more toxic nitrite form at higher rates than in older children or adults. The EPA also sets a combined limit of 10 mg/L for nitrate plus nitrite together (measured as nitrogen), since nitrate readily converts to nitrite inside the body.
How the WHO Standard Compares
The World Health Organization sets its guideline at 3 mg/L measured as the nitrite ion, which works out to roughly 0.9 mg/L as nitrite-nitrogen. That’s slightly below the EPA’s 1 mg/L threshold. The WHO derived this number by starting with the known safe concentration of nitrate for bottle-fed infants (50 mg/L as nitrate ion), converting it to the equivalent nitrite concentration, and then applying a factor to account for the rate at which infants convert nitrate to nitrite in their digestive systems (estimated at 5 to 10 percent). Because the guideline already protects the most sensitive population, the WHO considers no additional safety margin necessary for the general public.
Nitrite vs. Nitrate: Why the Limits Differ
Nitrate and nitrite are closely related but not equally dangerous. Nitrate itself is relatively harmless. The problem starts when bacteria in your mouth and gut convert nitrate into nitrite. Because nitrite is the compound that actually damages hemoglobin, its safety limit is set ten times lower than the nitrate limit: 1 mg/L for nitrite compared to 10 mg/L for nitrate (both as nitrogen).
On a molar basis, 1 millimole per liter equals 62 mg of nitrate or 46 mg of nitrite. This matters if you’re comparing test results across different reporting formats. Home test kits and lab reports may express results as “nitrite-nitrogen” (NO₂-N) or as “nitrite ion” (NO₂⁻). If your result reads 3.3 mg/L as nitrite ion, that’s the same as 1 mg/L as nitrite-nitrogen, and you’re right at the federal limit.
Long-Term Exposure and Cancer Risk
Beyond the acute risk of methemoglobinemia, there are concerns about what happens when you drink low levels of nitrite over many years. Inside your stomach and intestines, nitrite-derived compounds can form substances called nitroso compounds, some of which are carcinogenic. The International Agency for Research on Cancer classified ingested nitrate and nitrite that form these compounds as “probably carcinogenic to humans” (Group 2A) in 2010.
The current EPA safety limits were designed around the acute risk of methemoglobinemia, not cancer. The EPA released a protocol in late 2023 to reassess the health risks of nitrate and nitrite more broadly, but an updated risk assessment has not yet been published. For now, staying well below the 1 mg/L nitrite limit remains the best practical guidance.
Where Nitrite Contamination Comes From
Nitrite in drinking water typically originates as nitrate that gets converted through bacterial activity in soil or plumbing. Since the 1950s, nitrate levels in many water sources have climbed due to nitrogen fertilizer use, animal feeding operations, and fossil fuel combustion. Private wells in agricultural areas are especially vulnerable because of their proximity to fertilized fields and septic systems.
Public water systems are required to test for nitrite and treat water that exceeds the limit. Private wells have no such requirement. If you rely on a private well, particularly in a farming region, the responsibility to test falls on you.
Testing Your Water
You have two main options for checking nitrite levels. Home test kits use color-change strips or reagent drops and can detect nitrite at low concentrations, though their precision varies. For a definitive number, a certified laboratory analysis is more reliable. Many state health departments offer free or low-cost well water testing, and county extension offices in agricultural states often run seasonal testing programs.
If you’re on a public water system, your utility is required to publish an annual Consumer Confidence Report that lists nitrite and nitrate levels alongside the federal limits. You can usually find this on your water provider’s website.
Reducing Nitrite if Levels Are Too High
Three treatment methods are EPA-approved for removing nitrite from drinking water: ion exchange, reverse osmosis, and electrodialysis. For home use, a point-of-use reverse osmosis system installed under your kitchen sink is the most common and accessible option. These systems push water through a membrane that blocks nitrite and nitrate along with many other contaminants.
Boiling water does not remove nitrite. In fact, it concentrates nitrite by evaporating some of the water. Standard carbon filters, like those in most pitcher-style water filters, also do not remove nitrite effectively. If your well tests above 1 mg/L for nitrite or above 10 mg/L for nitrate, a reverse osmosis unit or connecting to a treated public water supply are the most practical solutions. For households with infants, switching to bottled water for formula preparation is a reasonable short-term measure while addressing the underlying contamination.