More than 62 million Americans may be unknowingly drinking tap water contaminated with a hidden toxin linked to cancer, birth defects and organ damage, experts warn. Nitrate is a colourless, odourless and tasteless pollutant that can seep into household water supplies from farm fertiliser and animal waste.
Because it has no smell or flavour, most people would have no idea it is in their glass. Researchers now say one in five Americans served by more than 6,000 community water systems received drinking water that tested at concerning nitrate levels at least once. They add that households in nitrate hotspots should consider using water filters to reduce exposure.
The warning comes as scientists say the federal legal limit for nitrate is badly outdated. The current cap is 10 milligrams per litre (mg/L), a limit set in 1962 after nitrate-tainted water was linked to 'blue baby syndrome' – a rare but potentially fatal condition that starves babies of oxygen. But since then, studies have linked nitrate exposure at far lower levels to multiple cancers, preterm birth, low birth weight and birth defects.
The Environmental Working Group uses 3mg/L as a modern benchmark because it indicates pollution is present and may already pose health risks. One in five Americans served by 6,114 water systems drank water that tested at or above 3 mg/L for nitrate at least once. Some communities recorded levels far above that threshold. In Garden City, Kansas, tests detected nitrate at 37mg/L – nearly four times the federal legal limit. In Fresno, California, water systems logged more than 2,600 tests at or above 3mg/L between 2021 and 2023. In June last year, nitrate levels in Iowa’s Raccoon River climbed to 20.55mg/L – more than double the legal limit and the second-highest reading on record.
The problem is not limited to farming states. On Long Island, near New York City, the Westbury Water District recorded nitrate levels as high as 6.20mg/L in groundwater serving more than 20,500 people. San Francisco also found widespread contamination, with nearly 80 per cent of tests showing nitrate at or above 5mg/L. Experts say this shows nitrate pollution can affect suburban and urban areas as well as rural communities.
Not everyone faces the same risk. Infants under six months old are considered especially vulnerable because their bodies cannot properly process nitrate. If formula is mixed with contaminated water, nitrates can interfere with the blood’s ability to carry oxygen, triggering blue baby syndrome. Pregnant women may also be at increased risk. Studies have linked nitrate exposure during pregnancy to preterm birth, low birth weight and neural tube defects such as spina bifida. People who rely on private wells face another danger because their water is not routinely monitored or regulated by federal agencies. If they live near farmland, they may be exposed to high nitrate levels without realising it.
Researchers say three major trends are making the problem worse. The first is climate change. Heavier rainfall and stronger storms increase runoff from farm fields, washing more fertiliser and manure into rivers, streams and groundwater. Drought can also intensify contamination. When rain finally returns after a dry spell, built-up nitrogen can be flushed into water supplies all at once. Second, federal subsidies encourage farmers to keep planting corn – one of the most fertiliser-intensive crops – year after year. Third, the nitrate limit itself has not kept pace with modern science. It was designed to prevent blue baby syndrome, not cancers, thyroid disease and birth defects that later studies have associated with lower exposure levels. Meanwhile, efforts by the Environmental Protection Agency to reassess nitrate risks have reportedly stalled for years.
Several studies have also raised fresh alarm over cancer risks. In a 20-year study of nearly 22,000 older women, those who drank water containing nitrate above 5mg/L for five or more years had more than double the risk of thyroid cancer. Another study of nearly 35,000 older women in Iowa found those exposed to similar levels for four or more years had a 62 per cent higher risk of bladder cancer. And in a 27-year study of nearly 55,000 Danish adults, higher nitrate levels in tap water were linked to a 48 per cent increased risk of lower bowel cancer.
Experts say the simplest way for households to cut exposure is to check local water quality reports and use a certified filter designed to remove nitrate.
