The largest water utility in Iowa is sounding alarms that it won't be able to keep up with cleaning the water for more than 600,000 customers as extreme weather swings become more common.

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The largest water utility in Iowa is preparing for a wet spring after almost two years of drought. To do that, Des Moines has made costly upgrades to its treatment facilities. And other systems across the country may need to do the same. Iowa Public Radio's Clay Masters reports on how water quality issues add to some climate change problems in farm country.

CLAY MASTERS, BYLINE: While nitrate occurs naturally, it's also a byproduct of nitrogen fertilizer. And Iowa farmers use lots of that to grow their corn and soybeans. Nitrate finds its way into surface and groundwater that eventually becomes drinking water. Studies have linked ingesting too much nitrate in drinking water to cancer, and that concerns retired teacher Janis Elliott, who spent about a thousand dollars on a reverse osmosis system in her home in the small Iowa town of Avon.

JANIS ELLIOTT: So this is the safe water, just that little thing there.

MASTERS: Elliott started testing the water from her private well for nitrates about five years ago. The EPA health standard in the U.S. is 10 parts per million. What finally got Elliot and her husband to install this pricey device was when the nitrate level got up to 19 parts per million.

ELLIOTT: Which is almost double the federal legal limit for drinking water. So we were drinking poison for a year.

MASTERS: Larger water utilities have been treating this problem for years. Take Des Moines Water Works, for example. It gets most of its water for its 600,000 customers from the Raccoon and Des Moines rivers. Ted Corrigan is the utility's CEO and says last summer, there were toxins on the Des Moines River that made it unusable. Add to that, climate change is creating another problem.

TED CORRIGAN: We also see issues with the quantity of nutrient that is stored on the landscape because of the drought. Now we have excess nutrients in the soil. We hope for rain. But if it does rain, we have the potential for extremely high nitrates. It's not a sustainable situation.

MASTERS: Water Works has upgraded its facility and constructed deep wells to store more water. And it's looking at building additional groundwater wells. More than 90 miles upstream from Des Moines, Mark Schleisman farms with his father and kids in Calhoun County near the Raccoon River. He's showing me a large wetland on his property that hooks up to an irrigation system so he can reuse the water on his land.

MARK SCHLEISMAN: This is something that we can say yep, it helps the river because we're keeping the nitrates here, reducing them. But it also helps me because I'm getting water on this field, and I'm getting - I'm reusing the nitrogen, also.

MASTERS: Schleisman says farmers know what tools to use, but they're costly and can be cumbersome. While politicians here insist Iowa is making good progress with nitrate in water, University of Iowa Geographical and Sustainability Sciences professor Silvia Secchi disagrees. She argues that the federal farm bill essentially subsidizes farmers to pollute.

SILVIA SECCHI: What we need to do is we need to ask for some environmental outcome for all the money we give to farmers, and that will reduce the load so that the utilities don't have to spend so much money cleaning up the water that we drink.

MASTERS: And Secchi says it's a bigger concern for utilities in smaller cities and residents who rely on their private wells that may have nitrate-tainted water. The challenges in Iowa are similar to those in other places surrounded by farmland, especially as they increasingly face drastic weather swings that affect drinking water. For NPR News, I'm Clay Masters in Des Moines.

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