Warming Winters Exacerbate Nitrate Pollution in Iowa Drinking Water

Climate change is making the water quality problem even worse for Des Moines and other agriculture-dependent communities.

Apr. 1, 2026 at 1:40pm

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Nitrate pollution from fertilizers and pesticides is a persistent issue for Iowa's drinking water, and warming winters are making the problem worse. When the ground doesn't stay frozen, more of these chemicals get washed into rivers and streams that supply drinking water, forcing cities like Des Moines to spend thousands of dollars a day to filter out the dangerous nitrates. Experts say this trend is likely to continue as climate change brings more extreme weather and unpredictable precipitation patterns to farm country.

Why it matters

Nitrate pollution in drinking water can pose serious health risks, especially for infants and young children. As climate change drives more winter thawing and rain-on-snow events, the costs of managing this pollution will continue to rise for municipalities and private well owners, disproportionately impacting low-income rural communities. Addressing the root causes of this issue, such as regulating agricultural runoff, will be crucial to ensuring safe and affordable drinking water for Iowans.

The details

Nitrates from fertilizers and pesticides used by Iowa's farmers routinely end up in the Raccoon and Des Moines rivers, the main water sources for the state's capital city. When nitrate levels get too high, Des Moines Water Works has to run an expensive filtration system at a cost of around $16,000 per day. This year, the city had to filter in January and February - just the second time that's happened in over 30 years, a sign that warming winters are exacerbating the problem. As the ground thaws more often and snow melts rapidly, more of these agricultural chemicals are getting flushed into waterways, especially during intense rain-on-snow events. Scientists warn this trend is likely to continue as climate change brings more extreme weather to the region.

  • In January and February 2026, Des Moines had to filter its drinking water for nitrates, just the second time that's happened in over 30 years.
  • Experts say warming winters and more frequent rain-on-snow events are driving the increase in winter nitrate pollution.

The players

Justin Glisan

Iowa's state climatologist.

Trent Ford

Illinois' state climatologist.

Samuel Sandoval Solis

A professor at the University of California-Davis and an extension specialist in water resources management.

Carol Adair

A professor at the University of Vermont who has studied how rain-on-snow events could worsen nutrient pollution.

Dani Replogle

A staff attorney for Food and Water Watch, a nonprofit for sustainable food and clean water.

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What they’re saying

“We are more apt to see these in the future. Are they going to occur every year? No. But the ingredients are there for them to potentially occur more often.”

— Justin Glisan, Iowa's state climatologist

“In central and southern Illinois, we've always dealt with a sort of ephemeral freeze-thaw, freeze-thaw process. What we're seeing is that's really tracking farther north.”

— Trent Ford, Illinois' state climatologist

“There really are two paths. One is conservation efforts and responsible watershed practices. And the other is spending hundreds of millions of dollars in treatment solutions.”

— Amy Kahler, CEO and general manager at Des Moines Water Works

What’s next

Scientists are still studying the full ecosystem impacts of increased winter nitrate pollution, and municipalities like Des Moines are preparing resiliency plans to handle more frequent filtration needs. However, experts say the best long-term solution is for agricultural producers to implement more conservation practices to reduce runoff, rather than relying solely on expensive water treatment.

The takeaway

As climate change brings warmer winters and more extreme precipitation patterns to the Midwest, the costs of managing nitrate pollution in drinking water will continue to rise, disproportionately impacting low-income rural communities. Addressing the root causes through better agricultural practices is crucial to ensuring safe, affordable water for all.