Almost 20 samples from drinking water supplies in Donegal have failed inspections for an environmental pollutant this year.
It's the biggest failure rate nationwide with 59 concerns in total right across the country.
Irish Water has tested 791 samples nationwide to see if they were within the allowed limit of trihalomethanes which have been linked to cancer.
Glenties and Ardara accounted for the majority of failed inspections while areas in Letterkenny, Milford/Kerrykeel and Ballintra are also of concern.
Dr Michelle Minihan, from the Environmental Protection Agency, says the water is still safe to drink.