Central Iowa residents face a second consecutive summer banned from watering their lawns as Central Iowa Water Works seeks to preserve its capacity to produce sufficient safe drinking water.

CIWW announced the ban Monday, June 8, after Des Moines Water Works, its largest utility, estimated that with temperatures set to surpass 90 degrees Tuesday and high nitrate levels requiring it to provide additional treatment, demand would reach 98% of capacity.

Already, the system’s nitrate removal facility, among the world’s largest, was operating “at full throttle,” Des Moines Water Works CEO Amy Kahler said during a Monday news conference.

Here’s what to know about the ban.

Why is Central Iowa Water Works requiring a ban?

CIWW officials warned in early May that a lawn-watering ban like the one imposed in June 2025 was likely after a winter during which high nitrate levels in central Iowa’s source water — the Raccoon and Des Moines rivers — failed to abate.

Elevated nitrate concentrations in the rivers require “significantly more treatment” to achieve a federal safety standard of no more than 10 milligrams per liter, Tami Madsen, CIWW’s executive director, said at Monday’s news conference. Lawn watering greatly increases demand in warm weather, and “we have reached a point where conservation is necessary to preserve treatment capacity and ensure reliable service to everyone,” Madsen said.

Who does the ban affect?

Customers of Des Moines Water Works are the largest group. Also under the ban are Ankeny, Clive, Johnston, Norwalk, Polk City and Waukee and areas served by Urbandale Water Utility, West Des Moines Water Works, Warren Water and portions of the Xenia Water District.

Grimes, a member of the CIWW, isn’t under the ban because it’s not yet connected to the shared water distribution system.

How high have nitrate levels been?

In addition to the Raccoon and Des Moines rivers, the nitrate levels in the Des Moines Water Works’ infiltration gallery, a system of water naturally filtered through rock and sand, have been unusually high, Kahler said.

The gallery typically is the utility’s best water source. But it has been over the 10-milligrams-per-liter limit for nearly 90 days, which Kahler called a record.

On Tuesday, nitrate levels were 14.98 milligrams per liter in the Raccoon River; 11.75 milligrams in the Des Moines River; and 11.83 milligrams in the infiltration gallery, Des Moines Water Works reported.

Nitrates, even at low levels, have been tied to some cancers and to serious illness in infants. The federal government requires water utilities to alert consumers when nitrate levels rise above the standard. 

What’s causing high nitrate levels in the Raccoon, Des Moines rivers?

Farming contributes about 80% of the nitrates in the Raccoon and Des Moines rivers, according to a Polk County water analysis released last year.

Iowa farmers use commercial nitrogen as well as manure from millions of pigs, chickens, turkeys and other livestock to fertilize the state’s roughly 24 million acres of corn and soybeans. Nitrogen and phosphorus, two nutrients that can befoul Iowa waterways, also naturally occur in Iowa’s rich soil.

Weather plays a major role. Drought, for example, can result in a buildup of nutrients in the soil. When rains return, as they have the past two springs, they can pick up the contaminants and move them to waterways both over land and through the drainage tiles that underlie about 13 million acres of farm fields across Iowa.

What’s being done to cut fertilizer losses?

The state adopted the Iowa Nutrient Reduction Strategy in 2013, setting a goal to cut by 45% the nitrogen and phosphorus that reach Iowa streams and ultimately flow into the Mississippi River, contributing to the dead zone around the river’s mouth in the Gulf of Mexico, renamed the Gulf of America by the U.S. government.

The state and federal governments offer farmers financial and technical assistance to adopt practices like planting cover crops and reducing or eliminating tillage to cut fertilizer losses. They also encourage establishing buffer strips, bioreactors and wetlands that help clean water as it leaves fields.

More: With billions invested in farm conservation, is Iowa’s water cleaner?

In May, Gov. Kim Reynolds announced the state will give CIWW a $25 million grant to expand and upgrade its nitrate removal facilities, part of a statewide overhaul of Iowa’s water quality funding. However, the state so far has declined to impose measures to reduce nitrates from agricultural runoff, with Reynolds saying in July 2025 that regulation “is hardly ever the answer.”

Are candidates addressing the issue?

Zach Lahn, the GOP nominee to replace retiring Republican Reynolds in this fall’s gubernatorial election, has said Iowa must “start addressing the problem at the source — not just relying on expensive treatment upgrades after the damage is already done.”

“Upgrading water treatment facilities may help in the short term, but it’s ultimately a Band-Aid approach that passes massive costs onto taxpayers and communities,” Lahn said in a post on Facebook.

Democratic nominee Rob Sand points to improved water quality as part of an effort to address Iowa’s growing cancer rate, and calls for a variety of initiatives including tax breaks for farmers who adopt conservation measures, improved water monitoring and more transparent tracking of farmers’ manure use.