Two private water supplies in Kerry were found to be contaminated with E.coli last year.
The Environmental Protection Agency's Drinking Water Quality report for 2021, found failures by private group schemes (PGS) in Kells and Toor.
The EPA's annual report covers over 380 group water schemes, along with more than 1,700 small private supplies (SPS) around the country.
These private water supplies serve food businesses, nursing homes, crèches and B&Bs.
The agency says it put the health of approximately 6,000 people that use these drinking water supplies throughout the country at risk.
The report found that the PGS in Kells and Toor in South Kerry, had supplies with E coli.
Nationally, one in 20 private water supplies were found to be contaminated,
Meanwhile, the PGS in Tousist was found to have failures with trihalomethanes (THMs)
These are chemicals which are formed by the reaction of naturally occurring dissolved organic material in the water and chlorine, which is used for disinfection purposes.
The EPA says THM levels should be kept as low as possible and in compliance with the drinking water quality.
Elsewhere, the PGS in Bonane was listed on reasoned opinion for THMs.