Coleraine Borough Council has extended opening hours at the town's leisure centre until 2200 GMT tonight (Wednesday).
200 people have already been to Coleraine Leisure Centre for emergency drinking water and washing facilities.
The Council appealed to residents to check with their elderly and vulnerable neighbours to see if they need water.
Environmental Health Officers said they were trying to establish when the water supply would be restored to normal.
People who need water should bring their own containers to take it away.
Kieran Doherty, Coleraine's Director of Environmental Health, said that it was important for people to show community spirit by checking on elderly and vulnerable neighbours.
"In real terms people have been without water for four or five days, which makes it difficult to have the lifestyle we expect," he said.
"There's been a whole range of stories from people who haven't had a cup of warm tea for days, or haven't washed for four days."