The towns of Randles in Cape Girardeau County, Perkins in Scott County and Painton in Stoddard County are under a boil-water advisory until 5 p.m. Saturday.
Tap water intended for drinking, food preparation, making ice and brushing teeth should be boiled for at least three minutes.
"We have had a terrible power loss here. We spent the entire day searching for a generator to put on the pump an old water line system," said Bill Knoderer, board member of Stoddard County Water District No. 2, which serves all three communities.
The generator powers the water pump but does not extend to the district's chlorinating system.
More than 200 people are still without power in the city of Perkins.