Despite public assurances from Des Moines Water Works (DMWW) stating tap water nitrate levels remain below the federal safety threshold, independent at-home testing may indicate levels may exceed the 10mg/L legal limit for nitrates.
What nitrate levels are considered “safe”?
Des Moines Water Works has stated nitrate levels in central Iowa tap water are at 8.11 mg/L at the Fleur Drive Treatment Plant, and 8.09 mg/L at the McMullen Treatment Plant as of July 2, 2025. They have acknowledged raw water nitrate levels from both the Raccoon and Des Moines Rivers are near historic highs—20.55 mg/L and 17.15 mg/L, respectively—well above the EPA’s maximum contaminant level.
To mitigate risk, they have engaged its nitrate removal facility continuously for over 50 days. However, the facility can only treat up to 10 million gallons per day. Because summer demand often exceeds 70 million gallons, water passing through the nitrate removal facility is blended with water that goes through the normal treatment process to meet the federal drinking water standard.
The EPA has set an enforceable standard called a maximum contaminant level (MCL) in water for nitrates at 10 parts per million (ppm) (10 mg/L)
At-Home Test Exceeds 10mg/L
A new independent testing sample, exclusive to IowaPodcast.com, indicates nitrate levels in tap water may exceed the 10 mg/L line. A verified listener submitted the test image, obtained from a home tap water supply within Ankeny, Iowa.
It’s important to note at-home testing kits may not be as reliable as tests done in a lab setting—but caution is warranted.
Central Iowa residents should test their tap water, and/or filter it if they have concerns. Infants, women who are pregnant, and anyone with health conditions should exercise additional caution due to high nitrate levels.
Polk County did not immediately return a request for comment sent at 1:03pm CT 7/4/25. We will post a response when available.