It is claimed some plants were not designed to treat 'raw' water
Irish Water is warning that some 250,000 homes may face boil notices.
The utility says that more than half of its drinking water treatment plants - 472 - are at risk of failure.
These tend to be smaller treatment plants, operating above capacity or drawing water from a poor quality or 'at risk' source.
New quality guidelines mean that water will be tested up to six times a year, and that Irish Water can shut down plants and issue notices if a problem emerges.
"It is possible that more boil water notices will have to be issued, even in places where no problem appears to exist today," a spokeswoman told the Irish Independent.
"We're now finding problems which existed before, but were never picked up". This is due to increased sampling, which had not happened before.
It is also claimed that some plants built in recent years were not designed to treat the kind of 'raw' water they were dealing with.
Paul Melia is the environment editor with the Irish Independent, who broke the story.
He told the Pat Kenny Show here on Newstalk the findings are not totally surprising.
"A lot of the stuff with Irish Water about the problem on the network is just variations on a theme - the more they learn, the more investigations they do with the network, the more problems they find" he said.
"That's as you would expect - because for the first time we've actually had this root and branch look at what the state of the network is that we never had before".
"Before, it was much more piecemeal - each authority looked at their own network" he added.