DES MOINES, Iowa — A highly anticipated two-year water quality study by Polk County was released Tuesday, confirming that the nitrate in the river water is mostly due to agriculture.

The Central Iowa Source Water Research Assessment was commissioned in 2023 to offer unbiased and comprehensive examination of the watersheds for the Des Moines River and Raccoon River. It revealed that nearly 80% of the nitrate in those rivers is directly tied to agriculture.

The report says that “the rivers often contain some of the highest nitrate levels in the U.S. and routinely exceed the health-based drinking water standard, threatening human health and increasing the cost and complexity of water treatment.”

It also says livestock manure is produced in quantities unable to be fully absorbed as fertilizer, leading to the excess contaminating water.

The study outlines two dozen recommendations to improve water quality, like increased state funding for wastewater treatment facilities.

On Tuesday morning the report was received by the Polk County Board of Supervisors and then released to the public. 

“Having this comprehensive report is a way to address this problem. We know that it is going to be a multibillion-dollar program and a generational challenge to change the course that we’re currently in as a state,” Polk County Board Chair Matt McCoy said. “So we’re hoping this report will serve as an opportunity for interest groups and advocacy groups to work together to address the changes. There are action steps in this report that both those advocacy groups and community groups can take to try to impact change, that we want to clean up our water.”

Meanwhile, Central Iowa Water Works provided an update Tuesday, heading into the holiday weekend where people will be engaging in outdoor water activities. That is mostly okay, but the lawn watering ban is still in effect. They also want to clarify that you can still use water to cook, like boiling water. 

“All water produced by CIWW meets all safe drinking water standards. So right now, and all along water, has been safe for drinking, cooking and any other household use,” CIWW Executive Director Tami Madsen said. “Playing in slip n’ slides and filling kiddie pools are very insignificant fractions of that amount of our capacity. We do know we can handle that amount of water on our system capacity.”

In the latest tests, the nitrate in treated water at the Fleur and McMullen treatment plants are 7.21 mg/L. It is 15.19 mg/L in the Raccoon River and 12.07 mg/L in the Des Moines River. 

The treated water is still considered safe because it is under 10 mg/L. 

However, in this Polk County report, they said in their research that some groups have 5 mg/L as an acceptable nitrate threshold. There is no consensus on what it should ideally be. 

CIWW responded to this saying, “the EPA sets the drinking water standard to 10mg/L. That’s re-evaluated in a regular interval. That’s been re-evaluated within the last two years. The EPA continues to maintain the standard at 10 mg/L. That’s the standard that we treat too,” Madsen said.

For more information and to read that water research report by Polk County in full, you can visit PolkCountyIowa.gov.

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