DES MOINES, Iowa (AP) — In the dim light just after dawn, Bill Blubaugh parks his Des Moines Water Works pickup truck, grabs a dipper and a couple plastic bottles and walks down a boat ramp to the Raccoon River, where he scoops up samples from a waterway that cuts through some of the nation’s most intensely farmed land.

Each day the utility analyzes what’s in those samples and others from the nearby Des Moines River as it works to deliver drinking water to more than 500,000 people in Iowa’s capital city and its suburbs.

“Some mornings walking down, it smells like ammonia,” he said. “It’s concerning. I’m down here every morning and care about the water.”

Water Works for years has tried to force or cajole farmers upstream to reduce the runoff of fertilizer that leaves the rivers with sky-high nitrate levels but lawsuits and legislative lobbying have failed. Now, it’s considering a drastic measure that, as a rule, large cities just don’t do — drilling wells to find clean water.

Small communities and individuals use wells, but large U.S. metro areas have always relied primarily on rivers and lakes for the large volumes of water needed. Surface sources provide about 70% of fresh water in the U.S., as a reliance on wells for big populations would otherwise quickly deplete aquifers.

However, the utility in Des Moines is planning to spend up to $30 million to drill wells to mix in pure water when the rivers have especially high nitrate levels from farm runoff, most likely in the summer.

After spending $18 million over the last two decades on a system to treat the tainted river water, it’s frustrating to pay out millions more for something other cities wouldn’t imagine, say utility officials.

“I look at it in disbelief,” said Ted Corrigan, the CEO and general manager of Water Works.