WASHINGTON – In 2015, Des Moines Water Works sued upstream counties to reduce manure and fertilizer runoff into the city’s drinking water supply, drawing attention to nitrate pollution. But nitrate contaminates water supplies throughout Iowa, according to a new report by the Environmental Working Group.

Eighty miles downstream from Des Moines, the city of Ottumwa is one of many communities in the Raccoon River watershed that face the same challenge of keeping nitrate levels in drinking water below the legal limit of 10 parts per million, or ppm, set by the U.S. Environmental Protection Agency. And in 2016, the Iowa Department of Public Health tested more than 1,700 private wells for nitrate. It found that 19 percent were at or above the legal limit of 10 ppm.

But the EPA standard is outdated and inadequate to protect public health. It was set 25 years ago to protect infants against blue baby syndrome and has not been reviewed since. More recent studies have found that drinking water with just 5 ppm of nitrate increases the risk of colon, kidney, ovarian and bladder cancers. In 2014 and 2015, average nitrate levels for tap water in 45 Iowa public water systems were at least 5 ppb.

Heavy rains wash nitrogen from excess fertilizer and manure off of fields and into surface waters in the form of nitrate. Almost three-fourths of the Raccoon River’s watershed – 1.7 million acres – is planted with corn, soybeans and other crops, and is treated annually with millions of pounds of fertilizer and other chemicals. The watershed is also home to 2.3 million hogs and 16 million chickens and turkeys, whose manure is applied locally.

Two of the most successful strategies to combat manure and fertilizer runoff are planting cover crops on fields after harvest, and planting buffer strips between row crops and the water’s edge. Using satellite imagery, EWG found that while there had been some modest gains in the number of acres on which farmers had planted cover crops, it was still less than 2.5 percent of the amount of needed to clean up the watershed. And similar satellite data showed a net loss in the number of acres buffer strips along fields that boarder streams within the watershed.

“Row crop agriculture and livestock operations are the leading sources of nutrient pollution in Iowa and other agriculture-intensive states,” said Soren Rundquist, EWG’s director of spatial analysis and author of the report. “While some farmers are taking steps to keep fertilizer and manure on the field, and out of drinking water supplies, a dramatic increase in funding is needed to help many more producers adopt these practices if we’re going to achieve any substantial improvement in drinking water quality.”

Congress must reauthorize the federal farm bill in 2018, which presents lawmakers with the opportunity to create a compact between farmers and taxpayers that implements some modest requirements for those who take support from taxpayers.

“Generous income subsidies through farm programs and crop insurance should come with strings attached,” said Craig Cox, senior vice president for agriculture and natural resources at EWG. “If farmers are going to get that level of financial support from taxpayers, they must be required to take simple steps to keep our drinking water clean.”