In the coming weeks, Irish Water will be writing to 140 thousand homes and businesses in 16 counties, where water supply is 'not as good as it could be'.
Homes and businesses on the public water network whose supplies are on the EPA's Remedial Action list will receive letters outlining problems with their supply.
Irish Water says the water is still safe to drink in 53 of the 55 water schemes in the list.
However, boil water notices are in place on the Lough Talt supply in Sligo and at Grangemore in Roscommon where the water is not safe to drink.
Irish Water will outline what they're doing in these 55 areas to improve supply, and how soon the works will be carried out.