Efforts to resolve THM issue on water scheme unsuccessful

A drinking water scheme in County Roscommon remains on the Environmental Protection Agency’s watch list despite being added more than four years ago.

The EPA told the Herald that Uisce Éireann’s attempts to solve the issue have been “unsuccessful”.

According to the EPA’s Drinking Water Quality in Public Supplies 2025 report, the North East Regional Water Scheme, which serves 8,759 people, was added to its remedial action list in the closing months of 2021. This was due to seasonal trihalomethanes (THM) exceedances, Uisce Éireann said.

These form when natural organic matter in the water source, such as vegetation, reacts with chlorine used in the disinfection treatment process. The HSE says there is scientific evidence that some of the individual THM chemicals could pose both short- and long-term health effects. However, there is insufficient scientific evidence to indicate that THMs cause cancer in people.

A spokesperson for the utility company said progress is being made. “Operational improvements have been made to the plant to mitigate these exceedances,” the spokesperson said. “These include process improvements as well as a pilot process, installed in 2025, which will inform the long-term design of the plant.” 

The EPA told the Herald that previous trials by Uisce Éireann to solve the THM issue on the North East Regional Supply have been unsuccessful.

“Uisce Éireann is developing a further action programme to solve the issue. The EPA continues to oversee Uisce Éireann’s response to this priority site," said an EPA spokesperson.