Two Cavan water supplies were identified as having persistent failures last year.
Both the Cavan Rural Water Supply Scheme and the Belturbet supply had persistent pesticide issues in 2018.
A Wexford supply was the only other scheme to have a reoccurring issue.
According to the EPA’s Drinking Water Report, 42 supplies were investigated for pesticide levels last year, down from 53 in 2017.
There were also two water restrictions in Cavan last year, in Shercock as a precaution and in Ballyhaise for nitrate levels at tap.
No issues were detected at any public water supplies in County Monaghan.