Floodwater has contaminated three of the city's four drinking water wells and residents are being asked to conserve.
The city plans to set up 10 checkpoints where residents will have to show ID and sign in before being allowed to return home to pick up belongings. Houses with severe damage will remain off limits.
In nearby Iowa City, the Iowa River is rising more slowly than expected. But it has already caused major damage to the University of Iowa campus, where more than 20 buildings have taken on water.