The Grey District Council has found and fixed the cause of a chlorine gas leak at its main water pumping station but residents are still being told to boil water.
The leak was at the Coal Creek pumping station, which supplies water to about 8000 people in Greymouth, Cobden, Blaketown and several other nearby settlements.
The chlorination plant at the pumping station had to be turned off on Friday morning while the cause of the leak was investigated, so all water in the district had to be boiled before drinking.
Grey District Council assets manager Mel Sutherland said the gas leak was potentially dangerous, but no one entered the building without breathing apparatus.
He said the leak was caused by the failure of a lead seal, which has now been replaced.
However Mr Sutherland said it's too early to stop boiling water and the boil water notice will remain in place until Saturday morning.
"Because we had to turn the chlorination plant off, the chlorine levels in the supply have dropped over time so we're asking for the boil water notice to stay in place until around 8am Saturday morning and the chlorine levels are back up to acceptable levels."