The Des Moines Water Works board on Thursday voted to give the required 60-day notice to three Iowa counties that manage drainage districts — Sac, Buena Vista and Calhoun —  that the utility intends to sue them under the federal Clean Water Act for allowing high levels of nitrates to pour into the Raccoon River, a key source of drinking water for 500,000 customers in the Des Moines area.

William Stowe, chief executive officer and general manager of the utility, said he’d like to see the state and/or the counties regulate fertilizer applications, issue permits to control the pollution, or take other action after 15 years of voluntary conservation efforts by farmers have failed to solve the problem.  Water Works sampled water in the three counties over most of last year and found levels at times were nearly four times the federal drinking water limit of 10 milligrams per liter.

Nitrates both occur naturally and come from crop fertilizers and human and animal wastes. They are associated with a condition that suffocates babies, and with a variety of cancers.

Des Moines’ tap water remains safe to drink, but the utility has had to deploy an expensive treatment process to keep it that way, Stowe said.

The lawsuit in federal court would be an unusual play by a municipal utility with potentially statewide impacts. In effect, Water Works would  be asking the court to treat drainage districts like sewage treatment plants and other so-called point sources of pollution, subject to permits that could dictate changes meant to reduce pollution. There are some 3,000 drainage districts in Iowa, designed to keep fields dry for planting. That means large tile systems that worsen pollution in rivers such as the Raccoon, which has been identified as one of the top sources of nitrate in the entire Mississippi River system.

The Iowa Nutrient Reduction Strategy, designed to address the problem, calls for specific  changes to sewage treatment plants, which are a minor source of the nitrates, but only voluntary efforts on the farms that account for the vast majority of the pollution. Stowe has threatened to sue for months, mocking the voluntary conservation efforts as ineffective.

Agriculture groups suggest a legal battle will slow progress and that the voluntary efforts and teamwork  among governments and farm interests are key to cutting the pollution.

Sean McMahon  of the Iowa Agriculture Water Alliance said the state’s voluntary Nutrient Reduction Strategy needs more time to work. He said some data have suggested sharp reductions in nitrates in places, and spikes that typically come when rain is heavy.

He added: “With 92,000 farms in Iowa, it’s difficult to fathom how a one-size-fits-all regulatory scheme would work, with varying soil types and weather patterns.”

The alliance represents the Iowa Corn Growers Association, Iowa Soybean Association and Iowa Pork Producers Association and is designed to help ramp up the voluntary efforts called for by the Nutrient Reduction Strategy.