(C) Iowa Capital Dispatch
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Data analysis: How do nitrate levels in central Iowa this year compare to last? • Iowa Capital Dispatch [1]

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Date: 2025-07-25

Central Iowa Water Works is phasing out of its first-ever lawn watering ban, which has been in place since June 12 on account of sustained high nitrate levels in source water rivers.

A comparison of nitrate levels in the Des Moines and Raccoon rivers, which feed plants in the CIWW system, shows nitrate levels were elevated nearly 40 more days in 2025 than in 2024.

Utilities must keep nitrate concentration levels below 10 milligrams per liter to remain compliant with safe drinking water standards set by the U.S. Environmental Protection Agency. This becomes difficult to fulfill when both demand on the system and nitrate concentrations in the source water are high.

Tami Madsen, CIWW’s executive director, said there are many factors that make 2025 worse, in terms of dealing with nitrate, than 2024. In addition to sustained, elevated levels in the rivers, the infiltration gallery at the Des Moines Water Works’ Fleur Treatment Plant has also been elevated. The infiltration gallery is a series of underground pipes that collects alluvial ground water through more than three miles in Water Works Park.

Beginning around June 8, 2025, all three of these sources were above 10 mg/L, meaning the plant couldn’t pull from less concentrated sources to dilute the higher concentrations.

Voluntary and then mandatory lawn watering bans were issued to significantly reduce demand on the system. The reduced demand meant CIWW facilities could process enough water within the federal limits to remain compliant.

Voluntary water restrictions were issued last summer as well, which along with dropping concentrations in the Des Moines River by early July, relieved the system.

Madsen said the system this year was also stressed because the timing of the nitrate peaks coincided with lawn watering season, which represents up to 40 million gallons of demand per day.

“This year is different from any other year in that all three of our water sources at the Fleur Drive Plant – the Raccoon River, the Des Moines River, and the infiltration gallery, were significantly higher than 10mg/L for 33 days between June 8 to July 15,” Madsen said. “This coincides with the time frame that water uses typically increases for the summer season.”

Finished water leaving the treatment plants has remained within the federal safe drinking water standards, or below 10 mg/L. High-nitrate water can lead to shortness of breath and blue-baby syndrome if consumed by infants.

Some environmental groups and research however, hold that this standard might be outdated and that adverse health outcomes can occur from continued consumption of water with nitrate concentrations below the federal limit. They argue there are links to cancers, pre-term deliveries or birth defects.

Water output from the L.D. McMullen Water Treatment Plant had finished water with concentrations above 5 mg/L from March 31, 2024, until July 25, 2024. The highest concentration during that more than 117 day period was 8.6 mg/L and the average was about 7.1 mg/L.

Finished water concentrations stretched higher than 5 mg/L in 2025 at the L.D. McMullen plant beginning March 15, 2025 and have not yet dropped below that mark. Since March 15, the average level has been 7.2 mg/L.

At the Fleur plant, nitrate concentrations remained above 5 mg/L from April 4, 2024 through July 29, 2024. The plant had a total of 117 days during the spring and summer with outputs higher than 5 mg/L and a high during the period of 8.97 mg/L. The average during the period was 7.48 mg/L.

According to Melissa Walker with Central Iowa Water Works, the nitrate removal facility ran for 68 days in 2024. As of Thursday, the removal facility has been running for 97 days in 2025.

The database for Des Moines Water Works does not log river data every day so there are fewer data points for the rivers compared to output from the facilities.

In 2024, the Raccoon River was above 10 mg/L for 64 days during the March-August time frame.

Levels rose above 10 mg/L on March 29, 2024, and remained above 10 mg/L, with periodic dips no lower than 7 mg/L until July 15, 2024. The average concentration in the river during this time period was 12.98 mg/L and the highest recorded concentration was 18.2 mg/L.

The Des Moines River did not have concentrations above 10 mg/l until April 29, 2024, though levels fluctuated from about 5 mg/L to 9 mg/L for the early part of April. In total, the Des Moines River had 41 days with concentrations above 10 mg/L.

During this time of elevated levels, the average concentration was 12.79, and the highest concentration measured 15.56 mg/L.

In 2025, levels in the Raccoon River first rose above 10 mg/L March 25 and remained above the federal limit through July 18, with 16 days during the period where levels dipped between 6 and 9 mg/L following significant rain events.

During the 91 day period of elevation, the average level was 12.82 mg/L with a maximum of 19.39 mg/L.

Nitrate levels in the Des Moines River didn’t jump above 10 mg/L until April 10 this year. Levels remained elevated above 10 mg/L until July 18, aside from periodic drops to around 8 mg/L following significant rain events.

The maximum recorded concentration in the Des Moines River was 16.6 mg/L this year and the average concentration during the 80-day period was 11.9 mg/L. There were 12 days during the period of elevation where levels dipped below 10 mg/L.

CIWW started the phased-in end to the lawn watering ban on Tuesday, following sustained downward trends in the source water nitrate concentrations. Under the phased-in approach, even numbered houses can water their lawns Sundays, Wednesdays and Fridays and odd numbered houses can water on Tuesdays, Thursdays and Saturdays.

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[1] Url: https://iowacapitaldispatch.com/2025/07/25/data-analysis-how-do-nitrate-levels-in-central-iowa-this-year-compare-to-last/

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