A boil water notice affecting up to 26,000 people has been imposed in Wexford town.
The notice was issued by Irish Water and Wexford County Council because of issues with disinfection in the supply.
Irish Water said that it and the council are working to rectify the issues "with a view to lifting the notice as quickly and as safely as possible".
The notice was issued following consultations with the Health Service Executive.
It advises customers on the Wexford town water supply to boil all water being used for drinking, making water-based drinks, or for washing salads or other foods which are not cooked before being eaten.
Irish Water said it is not necessary to boil water for handwashing.
Pat Duggan of Irish Water said public health is its "number one priority" and that staff are "working tirelessly" to resolve the issues affecting the treatment supply plant.