Drinking water in three supplies in Ireland - including Castlerea - was found to have at least 10 times the maximum allowable limit of lead last year.
Water in 23 supplies across the country were found to have above the permitted level, according to Irish Water's most recent inspections.
11 times the limit was detected in Dublin City Council's Leixlip supply - which serves much of the north and west of the capital.
Lead nearly ten times the limit was found in the Castlerea Public Water Supply in Co Roscommon, and there were similar results on the Roundwood Reservoir supply in Dun Laoghaire / Rathdown.
Irish Water says the exceedances arose from the presence of lead pipework within properties, and is therefore the owners' responsibility.
Environmental consultant Jack O'Sullivan says the results are a major concern: