DES MOINES, Iowa — Last week, Central Iowa Water Works placed a ban on commercial and residential lawn watering to avoid violating federal nitrate levels in drinking water.

On Tuesday, leaders with CIWW held a news conference updating current nitrate levels, and when they expect the levels to drop. Nitrate levels are nearing a historic high in both the Des Moines and Raccoon rivers, with the highest being in 2013. Leaders say that eliminating lawn watering is the most efficient way to help reduce water demand. Since enacting the ban, CIWW says they’ve seen a 30% reduction in water use.

CIWW stresses that the issue is a quality issue, and not a quantity issue, and that when concentrations are as high as they currently are, the amount of water they are able to process is slowed. CIWW says that its nitrate removal equipment is all running basically at capacity.
CIWW says that nitrate conditions are improving, with current levels of nitrate concentration being the highest at the Fleur Drive plant at 7.7 Milligrams per liter on Tuesday. The Environmental Protection Agency’s nitrate limit is 10 milligrams per liter.

Leaders with CIWW said that 90% of nitrates come from fertilizer from crops, but gave further explanation as to why we’re seeing this issue now.

“Well, in our experience, we see very high nitrate concentrations when we have average precipitation following dry periods,” Ted Corrigan, CEO at Des Moines Water Works, said. “We had an extended period of drought in 2020 through 2023. This spring we’re seeing average or normal precipitation patterns. Those two things combined to provide very high nitrates in our source waters, in our experience. So, that’s probably part of the reason.”

CIWW also touched on how the rain in the forecast this week could change the nitrate levels.

“Rain can be good or bad. Unfortunately, when it rains, it tends to extend the length of this event. If we have rain locally here, right in the metro, that tends to provide some relief, people get a little water on their grass, it keeps the temperatures down, demand stays down. Rain up in the watershed is another story. If we have moderate rain, that might dilute the nitrates a little bit initially, but it tends to wash more nitrate off of the landscape into the rivers and streams, raise those concentrations and extend the length of time that we’re in this event,” said Corrigan.

CIWW touched on future plans to help combat high nitrate levels in the future. Leaders showed plans for adding treatment capacity at the Saylorville treatment plant, West Des Moines, and expanding the Grimes plant to add 34.2 million gallons per day in treatment capacity, roughly 25 %. Those projects are expected to be complete within the next seven years.

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