A dangerous bacteria that can cause kidney failure was found in 62 private water supplies in 2018.
A new report found more than 1,000 people got a serious infection as a result.
The Environmental Protection Agency analysed private water supplies in Ireland in 2018, which serve more than a million people every day.
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 in 2018..
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.