Residents of Co Clare have been told to boil all drinking water and water for food preparation after the E.coli bug was detected at a treatment plant.
Clare County Council and Ennis Town Council said a "low level" of E.coli was found due to a malfunction of the chlorination equipment at the Drumcliff facility.
All water for drinking, food preparation, brushing of teeth and ice-making should be boiled, allowed to cool and stored in a fridge. This procedure should continue until further notice.
The council said water filters should not be used as a substitute for boiling and that water from the hot tap is not safe to drink.
The boil notice applies to Ennis Town, Clarecastle, Crusheen, Barefield, Doora, Drumcliff, Spancil Hill and all group water schemes served by the Ennis town supply.
The council said the problem has now been rectified.