Uisce Eireann is considering "Plan B" in Clifden as water is unlikely to be restored at 2pm as planned.
The works were originally set to be completed by midnight last night.
Tankers have been placed at various locations, but the water must be boiled before use.
The major leak on the Clifden Regional Supply Sceheme occurred on Monday.
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But crews are struggling to find the leak - and Councillor Eileen Mannion says a back-up plan is in place.
