Nitrates in Drinking Water: Health Risks for Clients

This handout was developed alongside our course, "OT, Nitrates, and Cancer Prevention," with Jesse E. Bell, PhD, of the University of Nebraska Medical Center. The episode looked at a 2022 study that linked groundwater nitrate in Nebraska counties to higher rates of pediatric cancer. Nebraska has one of the highest childhood cancer rates in the country, and families in farming areas have long worried about agricultural chemicals in their water.

The handout addresses a gap Dr. Bell described. In his team's survey of Nebraska healthcare providers, many said they knew little or nothing about nitrate. Most also said they wanted materials to help educate their patients. He also pointed out that families are often told to test their wells, then left without guidance when the result comes back high.

The two-sided design came out of that conversation. The first draft was a simple meter: green near zero, red at the federal limit of 10 mg/L. But research now links some health risks to levels below 10. Dr. Bell's advice was to show that risk works on a sliding scale, to be honest about what is still uncertain, and to avoid frightening people. The left side shows the established EPA reference points. The right side shows the emerging research.

The handout is built for prevention and risk-reduction conversations. It's most relevant for rural clients on private wells, since public water systems are required to meet the federal limit and private wells are not. It's also relevant for pregnant clients and for households with infants under six months who drink formula mixed with well water. That group is the one the 10 mg/L limit was designed to protect.

It works in primary care and home health. It also fits a care model discussed on the episode: a physician flags a family at risk and refers them to OT for a longer education visit and help with water testing. OTs in the home are well placed to walk families through test results, treatment options, and follow-up.

The left side of the scale comes from the EPA. The federal limit for nitrate in drinking water is 10 mg/L. It was set to protect infants from blue baby syndrome (methemoglobinemia), a condition where the blood can't carry enough oxygen. The EPA also notes that levels over 1 mg/L indicate human activity, and levels over 3 mg/L generally indicate contamination.

The right side summarizes newer research on long-term exposure below the federal limit:

• Pediatric cancers. A Nebraska study reviewed county data from 1987 to 2016. Counties with groundwater nitrate between 2.1 and 5 mg/L had higher rates of pediatric brain and central nervous system (CNS) cancers, leukemia, and lymphoma than counties at 0–2 mg/L (Ouattara et al., 2022).

• Colorectal cancer. A Danish study of about 1.7 million adults found higher colorectal cancer risk at nitrate levels well below current standards (Schullehner et al., 2018).

• Ovarian cancer. A National Cancer Institute study followed more than 25,000 women in Iowa and North Carolina. Most of them drank from private wells. Ovarian cancer risk rose as drinking water nitrate rose, but the estimates were imprecise and most were not statistically significant (Ammons et al., 2025). The authors say their results are consistent with the only earlier study on this question, which found higher risk in postmenopausal women in Iowa.

• Small for gestational age. (Spaur et al., 2025)

There is also a plausible biological explanation. Bacteria in the mouth convert nitrate to nitrite. In the stomach, nitrite can form N-nitroso compounds, which have caused cancer in animal studies. The Ammons study notes that these compounds cause ovarian cancer in animals.

These findings show associations, not proof of cause. Most of the studies are observational, and many can't separate nitrate from other contaminants or risk factors. The practical point for clients is that a result under 10 mg/L doesn't mean zero risk.

Use risk-reduction language. Treat this as a conversation about lowering risk, not preventing cancer. Some people with clean water still get cancer. That doesn't mean treating the water didn't help. Aim to inform without frightening, and respect the client's right to make their own decisions.

Bring the test results. If the client has a recent water test, find their number on the scale together. Start with the EPA side, then explain that the research on the right side is newer and still developing.

Check the units. Lab reports may list results as nitrate-nitrogen (NO3-N) or as nitrate (NO3). The EPA's 10 mg/L limit is measured as nitrate-nitrogen, which equals about 44 mg/L measured as nitrate. Reading the wrong unit can make water look much safer or much worse than it is.

Talk about next steps. A high result is more useful when the client knows what to do about it:

• Under-sink reverse osmosis system. It treats the kitchen tap and costs in the hundreds of dollars.

• Whole-house system. It runs into the thousands.

• Upkeep. Either system needs regular filter changes. It's a good idea to retest after installation, because very high contamination can overwhelm a system.

• Local help. In Nebraska, some Natural Resources Districts offer testing and reverse osmosis programs, and there is a state reverse osmosis tax credit. Confirm the current details before sharing them.