Irish Water is to write to 140,000 homes and businesses around the country to inform users about problems with their supply.
The letters will go to households who get their water from 55 "at risk" public water supplies.
The supply is drinkable but sub-standard in all but two of them, which are on a boil water notice.
The problems range from traces of pesticides in the water, to inadequate barriers for cryptosporidium.
Sean Laffey from Irish Water explains what customers will receive in the coming weeks.
"There will a covering letter and a booklet which will be specifically tailored to the water supply that a particular customer is on," he said.
"We'll be outlining the issues with the water supply, and why the water supply is on the Remedial Action List.
"We'll also be telling them what we're doing and giving them a timescale for the fixing of the problem."