Galway Bay fm newsroom - Four public water supplies in Galway recorded excessive levels of chemicals in 2016, according to the Environmental Protection Agency.
Trihalomethanes - THMs - are chemicals that can form when organic matter in the raw water, such as decaying vegetation, reacts with chlorine in the disinfection process.
The presence of THMs is minimised by Irish Water working to remove organic matter.
However, the latest report from the EPA shows 4 Galway public supplies still failed on THMs standard levels in 2016.
Boil notices and water restrictions were placed on 9 water supplies in Galway during 2016.
These include, Williamstown, Leenane, Kilconnell, Teernea/Lettermore, Loughrea, Carraroe, Ahascragh, Ballinasloe and Mid-Galway.
Nationally, 25 drinking water supplies around the country are at risk of being infected with cryptosporidium.
700 thousand people are served by these 'at risk' supplies, with nearly half of them based in Cork, Kerry and Donegal.
Darragh Page from the EPA says the risk of contamination with THM chemicals is a major concern.
