A boil water notice has been issued to residents in Gorey, Co Wexford.
It is estimated that some 7,500 people on the Gorey (Creagh) Urban Public Water Supply are affected.
Irish Water says that it is due to issues at the Creagh Water Treatment Plant, following heavy rains.
The utility says water must be boiled on a rolling boil for one minute, and then cooled for drinking, preparing drinks made with water, preparation of foods such as salads and other foods not cooked prior to eating, making of ice and brushing of teeth.
Areas affected are in the Gorey Hill, Gorey Corporation lands, Ramsford Park, Ballytegan, Clonattin Upper, Clonattin Lower, Gorey Bridge and Millands.
An investigation by the Environmental Protection Agency of the same water treatment plant in Gorey found that a power failure and a chlorine pump failure last August resulted in water leaving the plant, and entering the public supply without the appropriate level of disinfection.
There were 52 confirmed cases of illness associated with the Gorey outbreak, including bacteria linked to E. coli, at the time, with a number of associated hospitalisations.
Irish Water says it is not known at present when the notice will be lifted.
But the company says that it, along with Wexford County Council, are consulting with the HSE with a view to lifting it as soon as practicable.