The worms - ranging from a half-inch to an inch long - showed up earlier this week in the drinking water supply in Colcord, a small town about 80 miles east of Tulsa.
City councilman Terry Wood said city water was turned back on Wednesday morning after workers cleaned, drained and re-cleaned the water tower. No worms were found in the tower, he said.
"We are still looking into this problem. I mean we need to get to the bottom of it and we will continue to investigate and do pretty much what we need to do to find out what happened here," Wood said.
Residents are being asked not to consume the water or use it to brush teeth or prepare food, Wood said, but it can be used for showers and other activities.
Erin Hatfield, spokeswoman for the Oklahoma Department of Environmental Quality, said it's uncommon for red worms to show up in a water system in the state, though it's fairly common in the southeastern United States.
She's not sure why or how the worms wriggle into water systems.
There are no adverse health effects with the red worms, she said, and the DEQ provided Colcord officials with recommendations for their water system to prevent future red worm infestations.
Several businesses and organizations, like Walmart and the Cherokee Nation, have donated bottled water for residents in the 815-person town to use, Wood said.
"We've had situations before where we've been out of water," he said. "We've just had to use bottle water for consumption, so I don't guess it's been comfortable for some people but the last few hours haven't been that bad."
Colcord Public Schools canceled classes Wednesday, but Superintendent J.D. Parkerson said teachers and students are eager to return to classes Thursday, though no official decision has been made.
Health officials have provided guidelines to school administrators to make sure the schools are safe for the approximately 650 students.