More than 100 private water supplies failed to meet the bacterial standard for drinking water in 2019.
The Environmental Protection Agency says it's a serious issue that's putting people's health at risk.
In Donegal, two private group schemes were found to be non-compliant they were Townawilly and Ballymagroarty.
Meanwhile, the small private water supply at Gallagher's Bakery, Ardara was also found to be non-compliant.
Senior water inspector at the EPA, Dr. Michelle Minihan has confirmed that action has since been taken to remedy THM levels in all schemes in Donegal:
The full report can be accessed here