Iowa's largest water utility is threatening to sue three rural counties for allowing excess farm chemicals to contaminate drinking water, a dispute that is triggering a wider debate over the best way for Midwestern states to stop pollution from fertilizer runoff.

The Des Moines Water Works' action is being closely followed by environmental advocates and could have far-reaching implications for states like Minnesota that have battled similar threats to drinking water.

Leaders in Iowa's $30 billion agricultural industry, many of whom rely on nitrogen to fertilize crops, are railing against the move and say the problem requires cooperation with farmers, not more regulation. Gov. Terry Branstad has even accused Des Moines of declaring war on rural Iowa.

But officials at the Des Moines utility, which spends as much as $7,000 a day on a special treatment to remove nitrates from drinking water, say they're just doing their job.

"In this state, obviously, industrial agriculture is king," said Bill Stowe, CEO and general manager of the utility. "We'll continue to get a lot of blowback, but our ratepayers are first and foremost in our minds and they're tired of paying for other people's pollution."

Minnesota, too, struggles with high nitrate levels in rivers and groundwater, mainly in southern counties, but regulators here have favored a collaborative approach with farmers over legal action.

Four years ago, Deborah Swackhamer, a University of Minnesota water quality researcher, presented the Legislature with a 25-year plan to clean up the state's waters and recommended stricter pollution limits for farmers. She noted last week that nitrate levels in Minnesota waters are still rising.

"[There's] a lot of concern [about] how long would it take for the voluntary approaches to actually show a difference," she said. "And do we have time to do that? Iowa has said, 'No, we don't have time.' "

Who regulates farmers?

Des Moines Water Works wants to sue the three counties under the federal Clean Water Act. It claims that the 10 drainage districts they oversee in northwest Iowa should do more to stop the discharge of pollutants into the Raccoon and Des Moines rivers, key sources of drinking water downstream. The utility wants them to obtain federal permits that would limit the nitrates that go into the system.

Excess nitrates in drinking water can poison and kill infants, in addition to other potential health risks.

Many farmers in Iowa and Minnesota rely on a system of drain tiles — small underground tubes — to carry excess water from their fields, especially after heavy rains. When farmers apply fertilizer to crops, nitrates dissolve into the soil and seep into rivers and streams.

It's a problem all along the Mississippi River that has led to hypoxia, or low oxygen levels, in the Gulf of Mexico, harming aquatic life.

In recent years, Iowa has been working on a nutrient-reduction strategy that calls for voluntary cooperation by farmers, much like Minnesota and other states. Iowa's program has distributed millions of dollars to help farmers take steps like planting cover crops or buffer strips that curb soil erosion and chemical runoff.

Stowe said that isn't enough. He said recent monitoring of sites in Buena Vista, Sac and Calhoun counties shows nitrate levels as high as four times the federal limit.

If the problem continues, the utility would need advanced new equipment costing at least $85 million, and Stowe blames some of its recent rate increases on the additional treatment costs.

The dispute also raises broad questions about who is responsible for protecting the nation's water supply from agricultural pollution. Most farm runoff is exempt from federal regulation because it's considered "non-point-source" pollution, meaning it can't be traced to one source.

The utility, representing a half-million people, wants the courts to hold the drainage systems to the same standard as "point-source" polluters, or those whose origin is more easily traced.

Swackhamer said the Des Moines utility is using an interesting strategy by exploiting a loophole in the Clean Water Act. It argues that once water moves through a tile drain and is discharged, it's no longer free-flowing surface runoff and therefore no longer exempt under federal law from a permitting process.

Swackhamer said there would be "huge implications" for states like Minnesota but also for the U.S. Environmental Protection Agency to figure out how to actually regulate it.

Costly trial?

Farm groups and other critics say Stowe's approach is a legal stretch — ineffective in addressing water quality and likely to lead to even more delays as the matter gets tied up in court.

"To me, this is about a choice of how we improve water quality, and I believe we improve it faster by engaging folks, building that based on new technologies and … tapping into that innovation of farmers," said Bill Northey, the Iowa secretary of agriculture.

He said momentum is building in the state's voluntary nutrient reduction strategy. "You don't just snap your fingers and make it, you've got to build the infrastructure and interest," Northey said. "We think it's going the right direction, and we certainly don't want to undermine that."

John Tobert, head of the Iowa Drainage District Association, said drainage districts have no authority to regulate pollution. He said they're only in charge of maintaining the infrastructure.

Tobert said he doesn't think Des Moines Water Works will prevail, but people worry about what could be huge legal costs for expert witnesses and Washington, D.C., lawyers.

Wayne Fredericks, who plants corn and soybeans on nearly 1,000 acres just south of the Minnesota border and is president-elect of the state's soybean association, said it would be harder for farmers in the coming year or so to afford the expense of nitrate prevention practices, given that little profit was expected in the coming crop. While he plants cover crops on his farm in Osage, he said there hasn't been enough state funding for every farmer to afford it.

Fredericks said the utility's threat has raised awareness of the state's nitrate problem.

"People are listening," he said. "People are looking at what can we do in our farms."