Of the main nutrients in nitrogen, phosphorus and potassium (NPP) fertilizers, nitrogen in the form of nitrate is the most common cause of degradation of groundwater near agricultural lands. Nitrate pollution also arises from the excessive application of animal or human excreta to the catchment of the aquifer. Not only are excess nitrates dangerous to human health, leading to brain damage and even death in some infants (OECD 1994), but they stimulate rapid algal growth in waterways, leading to eutrophication in both inland waters and the sea.
A 2016 report, released by the Iowa Environmental Council (IEC), summarized 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.
Nitrate pollution from excess fertilizer use is now one of the most serious water quality problems. Maximum allowable levels of nitrates in drinking water are exceeded in some places in every country in Europe (OECD 1994) and in many countries in other regions. In some parts of Africa, nitrate loads in some suburban groundwater wells are 6-8 times WHO acceptable levels.
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 takes decades to reach an acceptable level 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 under the EEC/EU Directive on Drinking Water.
In the United States, more than 40 million people obtained their drinking water from a system in which there are violations of health-based standards, mainly those relating to nitrates. 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. 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.