What is Nitrate and nitrite* and Why Does It Matter?

Nitrate and Nitrite: A Common Contaminant With Serious Health Stakes

Nitrate is one of the most widespread contaminants in American drinking water — and one of the most misunderstood. It forms naturally in soil, but the biggest source today is human activity. Agricultural runoff carries fertilizer nitrogen into groundwater and rivers. Septic systems, animal feedlots, and wastewater discharge add more. Once nitrate enters a water source, it's colorless, odorless, and nearly impossible to detect without testing.

The health risks depend heavily on who's drinking the water. For infants under 6 months, nitrate is genuinely dangerous. It interferes with the blood's ability to carry oxygen, causing a condition called methemoglobinemia — sometimes called "blue baby syndrome" (WHO). In adults, long-term exposure is linked to increased risk of colorectal cancer, thyroid disease, and other health problems (EWG). Nitrite, a closely related compound that forms when nitrate breaks down, carries similar risks. Pregnant women and people with certain enzyme deficiencies face heightened vulnerability at lower exposure levels.

The EPA's legal limit for nitrate in drinking water is 10 parts per million (ppm). That standard was set in 1991, primarily to protect infants from blue baby syndrome. But the EWG's health guideline is far more conservative — just 0.14 ppm — based on more recent research linking lower nitrate levels to cancer risk. Across the 2,882 water systems where nitrate and nitrite were detected, the average level measured 0.862 ppm. That's well below the EPA's legal limit, but more than 6 times above the EWG health guideline. Even more striking: 2,079 of those 2,882 systems — roughly 72% — exceeded the EWG guideline. And at least one system recorded a peak of 13.5 ppm, dangerously close to the EPA's legal ceiling.

Geography matters a lot with nitrate contamination. The five states with the most affected water systems are Illinois (383 systems), Oklahoma (235), Missouri (181), Arkansas (175), and Ohio (158). That list isn't random. These states sit in the heart of American agricultural production. The Midwest's heavy corn and soybean farming depends on nitrogen-based fertilizers. When it rains, that nitrogen washes into rivers and soaks into aquifers. Illinois and Ohio, for example, draw heavily from groundwater sources that pass through farmland before reaching a treatment plant. Arkansas's poultry industry contributes significant nitrogen through animal waste. The pattern is clear: wherever intensive farming meets aging or limited water infrastructure, nitrate levels tend to climb.

The good news is that nitrate is very effectively removed by the right filtration technology. Standard carbon filters — including most pitcher filters and refrigerator filters — do not remove nitrate. You need a system specifically designed for the job. Reverse osmosis (RO) filtration removes up to 97–99% of nitrate from drinking water, making it one of the most reliable options for households. Ion exchange systems can also work well, particularly in whole-home applications. Echo Water's reverse osmosis systems are built to target nitrate along with dozens of other contaminants, giving your family clean water straight from the tap. If you're on well water in an agricultural area, testing your water at least once a year is especially important — private wells aren't regulated by the EPA and can carry nitrate levels that go unmonitored for years. Knowing your numbers is the first step. Acting on them is what protects your family.

Regulatory Standards for Nitrate and nitrite*

Cities With the Highest Nitrate and nitrite* Levels

States Most Affected by Nitrate and nitrite*

Frequently Asked Questions

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