The European Commission will take infringement proceedings against Ireland due to dangerous levels of chemicals found in drinking water.
The commission wrote to the Department of Housing this month confirming that a pilot case it had initiated into the level of trihalomethanes (THMs) in the water system has been closed.
In the correspondence, it confirmed that further “treatment” would now be necessary to deal with the chemicals, which have been linked to cancer.
A spokesman said the commission would now move to take “more formal steps” in response to ongoing concerns.
Sources confirmed that infringement proceedings would begin within a matter of weeks.
Ireland will be given the opportunity to respond to the action. If its response is inadequate, the commission can take the case to the European Court of Justice, whose judgment is binding.
Significant daily penalties could be imposed by the court if Ireland does not act appropriately.
THMs are chemicals that have been present in many public water supplies for years. They are formed when chlorine is added to purify water.
Long-term exposure is reported to carry increased risks of cancers, including of the bladder and colon, and causes damage to the heart, lungs, liver, kidney and central nervous system.
Permissible levels of trihalomethanes in drinking water are limited by the EU drinking water directive and World Health Organisation guidelines.
It is understood that up to 400,000 households in Ireland are affected, including ones in parts Kerry and Cork, Kilkenny city, Waterford, Wicklow, Meath, Mayo, Roscommon, Donegal and Galway.
In May 2015, the European Commission initiated a pilot case here due to THMs levels exceeding guidelines in some drinking water supplies.
A spokesman for the Department for Housing confirmed that correspondence had been received and said it would co-operate fully with the commission.
"Irish Water, working closely with the Department of Housing, Planning, Community and Local Government, has developed plans and programmes to address these THM exceedances where they have arisen," he said.
“These plans were communicated to the commission as part of the response to the pilot case.
“The commission informed the department last week that it has closed the pilot case but with the intention of further treatment.”
Irish Water said it was unaware of the commission’s response, but the company has already committed to addressing areas with THM by 2021.
Its business plan sets out a clear commitment to reduce the number of all schemes on the agency’s remedial action list, including those affected by trihalomethanes, “to zero”.
The Oireachtas is examining the future of water charges before a vote in the Dáil on March 13th.
A specially established committee will meet with the European Commission on February 15th to outline its response to the ongoing controversy.
Ireland has been warned it must meet its obligations under the EU Water Framework Directive or it could face additional action by the commission.
In its letter to the committee, it said Ireland must abide by the principle of making the polluter pay and the cost recovery principle.
The commission has urged the Government to charge for excessive and wasteful use of water through metering.