Irish Water has issued a precautionary boil water notice to more than 17,000 households in south Dublin and north Wicklow.
It said in a statement on Monday that high turbidity at a treated water reservoir at Vartry Treatment Plant meant a small amount of water was “inadequately disinfected” for a short period. Turbidity is the measure of how clear the water is, with a higher level indicating a greater number of particles in the water.
The utility said the water was still safe for washing but should be boiled for drinking, preparation of food and brushing teeth.
The Environmental Protection Agency has been notified of the incident.
Irish Water apologised for the inconvenience caused and said it was investigating the issue with a view to lifting the notice as soon as possible.
Customers in the following locations in Wicklow are affected: Newcastle; Newtownmountkennedy; Kilcoole; Kilpedder; Kilmacanogue Fassaroe/Berryfield Lane; Kilcroney; Delgany;
There are also rural areas between Callowhill and Cronroe which are affected including: Killiskey; Nuns Cross; Coynes Cross; Prospect; Mount John; Timmore Lane; Dunran; Ballyvolan and Kiltimon.
The following areas in Dún Laoghaire-Rathdown are also included: Ballyman, Kill Lane and surrounding areas.
Separately, a boil water notice in Longford has been lifted following completion of remedial works at Lough Forbes Treatment Plant.