More than half of the 900 drinking water supplies in the State are substandard and require remedial action if they are to provide adequate water to consumers year-round, Irish Water has said.
A two-year analysis of drinking water services conducted by the company found the number of substandard supplies in the Republic was more than three times worse than previously thought.
Past audits by the Environmental Protection Agency had led to 131 supplies being put on the remedial action list, whereas the Irish Water study found more than 450 supplies should be put on the list.
Irish Water said its more intensive sampling, begun in 2014, revealed difficulties in supplies to places such as Loughrea, Co Galway, and Whitegate, Co Cork, which had been overlooked.
A spokeswoman said part of the reason so many supplies were deemed substandard was because the Republic’s water supplies, unlike those in the UK, were based on surface water rather than ground water.
This meant they were more vulnerable to pollution, particularly during floods.
Moves to disinfect the supply using chlorine can give rise to the release of chemicals known as trihalomethanes, which have been linked to cancers.
Irish Water said it follows WHO guidelines which say concerns over trihalomethanes should never cause water to remain untreated.
The utility has plans for a €300 million upgrade to drinking water treatment plants to allow for the use of alternatives to chlorine.
The authority said the upgrade would be rolled out regardless of the controversy about billing, which has been suspended for domestic customers for nine months while a commission decides if or how the State should proceed with payments for water.
The spokeswoman said there had been no slippage in the authority’s multi-billion euro programme to bring drinking water supplies up to an acceptable standard by 2021, and that by then there should be no drinking water supplies on the remedial action list.
She said that “the Government has committed to supporting our funding this year” irrespective of the outcome of current discussions on billing.
The utility expects to spend about €500 million this year.
Irish Water said it had already upgraded or started construction on 100 water treatment plants and signed contracts for 319 new projects to improve water supply and wastewater treatment.