25 drinking water supplies around the country are at risk of being contaminated with cryptosporidium.
In its annual report, the Environmental Protection Agency (EPA) says more than 99% of drinking water samples complied with safety standards last year.
Specifically, microbiological compliance is better than 99.9%, while 99.5% of samples met chemical standards.
The EPA also says the overall quality of drinking water in public supplies remains high.
However, the agency warns that 87 supplies around the country need to be upgraded to avoid the risk of contamination by chemicals or infections - including 25 supplies at risk of being infected with cryptosporidium.
700,000 people are served by the 87 'at risk' supplies, with nearly half of them based in Cork, Kerry and Donegal.
Darragh Page from the EPA says a big problem in many supplies is the risk of contamination with THM chemicals.
He explained: "They are undesirable in drinking water, and anything above a standard of 100 is in breach of the European Drinking Water Directive.
"We have 58 of those supplies - serving over 400,000 people - that are in need of improvement."
He also noted that supplies in need of improvement are at risk of going on boil water notices: