DES MOINES, Iowa — On Tuesday, Central Iowa Water Works announced that both the Raccoon and Des Moines rivers recorded nitrate levels below 10 mg/L for the first time in weeks.

For nearly a month a lawn watering ban has been in place for customers served by Central Iowa Water Works after source waters, the Des Moines and Raccoon rivers, reached near record levels of nitrates. Officials with CIWW said the ban was necessary to ensure that water treatment plants could produce enough water that met the Environmental Protection Agency’s safe drinking standard for nitrates, which is 10 mg/L of nitrates or less.

CIWW Executive Director Tami Madsen said the ban has been successful, as it has reduced the strain on treatment plants by cutting demand by roughly 30%. Before the ban was implemented nitrate removal facilities had already been working at full capacity for several months, with peak demand at roughly 70 to 80 million gallons of water a day.

On Monday, CIWW loosened some restrictions by allowing sod companies to begin installing new sod through the use of tracking forms. Officials also told municipalities shortly after the lawn watering ban was implemented that they could reopen splash pads and spray grounds to normal operating hours after many voluntarily closed them.

CIWW said to fully lift the lawn watering ban, at least one water source must record nitrate concentrations at 10 mg/L or less. Recent rainfall has caused the nitrate levels to fluctuate in the Des Moines and Raccoon rivers. On Tuesday, officials said the Des Moines River measured 9.52 mg/L of nitrates, and the Raccoon measured 7.93 mg/L. Despite both the rivers measuring nitrate levels below the EPA standard, CIWW said the lawn watering ban will remain in effect until both rivers consistently measure a downward trend in nitrate levels.

According to CIWW, nitrate levels this year have been especially high due to several factors, but particularly due to years of drought. Officials said that due to little rain over the last several years, nitrates from fertilizers on fields didn’t run off, and instead built-up overtime until this year where Iowa has seen considerably more rainfall that’s washed the built-up nitrates into the rivers.

A recently released water quality study of the watersheds for the Des Moines and Raccoon rivers confirmed this, finding that nearly 80% of the nitrate in the rivers is directly tied to agriculture.

CIWW said it’s planning expansion projects at several water treatment plants to add more capacity to avoid an issue like this one in the future. Those projects are expected to be completed within the next seven years.

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