What is Nitrite* and Why Does It Matter?

Nitrite is a naturally occurring chemical compound that forms when nitrogen breaks down in soil and water. Most nitrite in drinking water comes from agricultural runoff — specifically from fertilizers and animal waste that seep into groundwater and rivers. It also enters water systems through the breakdown of nitrate (a closely related compound) by bacteria. Some industrial processes and septic systems contribute as well. Water treatment plants can introduce nitrite indirectly when they use chloramine disinfection, which can generate low levels of nitrite as a byproduct.

The health concern with nitrite centers on how it affects the blood. Nitrite interferes with hemoglobin, the protein that carries oxygen through your body. At high enough levels, it causes a condition called methemoglobinemia — sometimes called "blue baby syndrome" — where the blood loses its ability to carry oxygen effectively. Infants under six months old face the greatest risk because their digestive systems convert nitrite more readily and their hemoglobin is more vulnerable. Adults with low stomach acid, pregnant women, and people with certain enzyme deficiencies are also more susceptible. At the low average levels found in U.S. water systems — around 0.033 ppm — healthy adults are unlikely to experience acute effects. But long-term, low-level exposure is still an area of active research, particularly around links to certain cancers and thyroid disruption.

The EPA sets the maximum contaminant level (MCL) for nitrite in drinking water at 1 ppm. None of the 402 water systems where nitrite was detected currently exceed that legal limit. The highest recorded level in this dataset was 0.41 ppm — still below the EPA threshold. However, it's worth understanding what that limit was designed to do: it primarily protects against acute poisoning in infants, not long-term health effects from chronic exposure. The EPA's legal limits haven't been updated in decades, and some health researchers argue they don't fully account for cumulative exposure or sensitive populations. If you want a more conservative benchmark, the Environmental Working Group (EWG) recommends keeping nitrite levels as low as reasonably achievable, particularly for households with infants or pregnant women.

Geographically, nitrite shows up most often in states with heavy agricultural activity. Texas leads with 58 affected water systems, followed by Florida with 48, Iowa with 37, Massachusetts with 35, and Illinois with 34. The Texas and Iowa numbers aren't surprising — both states have intensive farming operations and significant fertilizer use. Florida's appearance on this list reflects its combination of agriculture, sandy soils that allow contaminants to leach quickly into groundwater, and a large number of smaller water systems that may have less treatment capacity. Massachusetts and Illinois are more urbanized, but both have rural agricultural zones and aging infrastructure that can complicate water treatment. Smaller community water systems, in particular, often lack the resources to monitor and treat nitrite as aggressively as large municipal utilities.

The good news is that nitrite is removable. Reverse osmosis (RO) filtration is the most effective method, removing up to 99% of nitrite from drinking water. Ion exchange systems — which swap nitrite ions for harmless ones — also work well and are commonly used in whole-house setups. Standard carbon filters, like pitcher filters or basic under-sink units, are not effective against nitrite. If you have an infant at home or are pregnant, this distinction matters. Echo Water's reverse osmosis systems are specifically designed to target nitrite along with dozens of other contaminants found in tap water. Boiling water does not remove nitrite — in fact, it can concentrate it as water evaporates. If you're in one of the top affected states and rely on well water, testing your water annually is a smart first step. Many county health departments offer low-cost or free testing. Knowing your actual levels lets you make a targeted decision about filtration rather than guessing.

Regulatory Standards for Nitrite*

Cities With the Highest Nitrite* Levels

States Most Affected by Nitrite*

Frequently Asked Questions

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