Water utilities warn of restrictions if nitrate levels stay high in the Des Moines and Raccoon rivers

It’s been a wet spring across Iowa, but water utilities in the Des Moines area are asking people to save water because nitrate levels are high in the Des Moines and Raccoon rivers.

The rivers are a major source for systems that are part of the regional Central Iowa Water Works, which provides drinking water to around 600,000 people in the Des Moines area.

Spring rains have driven nitrate levels in the rivers beyond the standard of 10 parts per million, set by the Environmental Protection Agency. This week, sensors on the Des Moines river and the Raccoon river showed levels around 15 or 16 parts per million.

That’s expected in a wet spring following a prolonged drought, according to Des Moines Water Works CEO Ted Corrigan. In dry weather, nitrates build up in the soils of farm fields upstream. Rainstorms are now flushing it downstream.

The levels in tap water are kept below the legal limit by mixing high-nitrate river water with low-nitrate sources such as water from wells, reservoirs and nitrate-filtering systems.

Des Moines Water Works started running its nitrate removal system nearly one month ago. Other members of the Central Iowa Water Works, which includes 14 metro and rural water systems, are putting more water into the system so that less high-nitrate water needs to be taken from the rivers. West Des Moines increased production at its main water treatment plant by 20%.

Corrigan said Des Moines Water Works is working to keep levels low.

“We're managing just fine right now, and the nitrate concentrations in the finished drinking water are actually fairly low. But what we're trying to do is anticipate what's going to happen when demand starts to build, and we're seeing demand start to increase,” he said.

Demand normally goes up in the summer, especially as residents and businesses start to water their lawns, according to Corrigan. Based on his estimates, if water use reaches its normal summer levels, those low-nitrate sources of water won’t be able to keep up.

“We just don't physically have enough nitrate removal capacity to remove all the nitrate we would have to remove at higher summertime demand,” he said.

As a precaution, members of the Central Iowa Water Works, which includes Des Moines, are asking people to voluntarily conserve and to not over-water their lawns.

“We may have to ask people not to water their grass until we get through this nitrate thing,” Corrigan said.

If nitrate levels in drinking water for customers exceed 10 parts per million, Corrigan said a notice would go out to all customers stating that infants under six months old should drink bottled water. The EPA’s threshold for nitrate is based on the risk of blue baby syndrome, although some researchers believe there may be health risks at even lower levels.

According to Corrigan, if the water comes close to surpassing the nitrate standard, the utility would take stronger steps.

“We would likely move to a mandatory measure which would prohibit lawn watering,” he said.