The residents of some 75 houses in the Moyola estate in Galway have been advised to stop using their water immediately, after the supply was found to be contaminated with kerosene.
It is understood that the contamination has been present for the past week.
Residents have been told not to use tap water for drinking, preparing food, brushing teeth, making ice or bathing.
They have also been advised that water from the tankers dispatched by the Council must be boiled before it can be used.