They found the quality of water in these sources - mostly sourced from wells - is poorer than in public supplies.
More than 60 private supplies were found to be contaminated with human or animal waste last year.
The dangerous bacteria E coli was found in 62 supplies.
This can cause illness and, in some cases, can result in severe or long-term kidney failure.
There were more than 1,000 cases of the VTEC infection - a dangerous form of E coli, which you get from drinking water contaminated with animal waste.
The EPA says Ireland has the highest incidence of this illness in Europe.
A failure of the disinfection system at the Vartry Reservoir in Wicklow caused 65,000 people in Dublin city to be put on a boil water notice early in the year.
Nitrate contamination also led to water restrictions in Kiltegan.
In Kildare, 26 private water supplies, cover a population of 3,965 people.
Kildare County Council audited 4 of those supplies in 2018, with no issues detected.