Nitrates are used in chemical fertilizers. When applied to fields much of nitrates often filter through the soil to the water table where they contaminate the drinking supply. Nitrates turn to nitrites in water and in human stomach and is suspected of causing stomach cancer and other diseases. In rivers, streams, estuaries and seas nitrates encourage the proliferation of algae, which stifle other, more various plants and fish.
According to a 1992 EU/ECE report, the nitrate content in groundwater in shallow wells in the Netherlands, Belgium, Denmark and Germany is above the acceptable drinking water limit and will only reach an acceptable level in 25 to 50 years' time under present management regimes. The concentration of 50mg of nitrates per litre of water is considered by the European Commission to be the maximum permissible level for water for human consumption.
The U.S. Department of Agriculture (USDA) estimates that removing nitrate from U.S. drinking water costs nearly $5 billion a year, which the industrial agriculture industry has been largely shielded from.
A 2016 report released by the Iowa Environmental Council (IEC) has attempted to summarize the related health risks of nitrates in drinking water. Researchers reviewed over 100 studies and found multiple studies linked them to birth defects, bladder cancer and thyroid cancer. While many of the health problems were found with nitrate levels higher than the drinking water standard of 10 mg/L, some studies suggested nitrate levels lower than the drinking water standard may still pose health risks. About 15 percent of private wells in Iowa may have nitrate levels that exceed federal standards. In 2016, the water utility in Des Moines, Iowa sued three counties, alleging they polluted the river with nitrates from agricultural runoff. The water utility has already spent $1.5 million to remove nitrates from drinking water, building arguably is the world's largest nitrate-removal facility, and wants fertilizer runoff to be regulated as pollution under the Clean Water Act. If the lawsuit succeeds, the agriculture industry will have to make changes to limit runoff.