Fears over lead contamination in the public water supply will be discussed by government ministers this morning.
Irish Water said any building that pre-dates 1970 has a good chance of being affected.
It is reported the heavy metal element has already been detected in the pipes leading to 75,000 homes, or 5% of the total around the country.
The problem is being described as a "public health risk", and will see a new grant rolled out for some low-income households to fund repairs.
The harmful metal is particularly dangerous to young children and pregnant women, so pipes in aging school and hospital buildings are also of concern.
Irish Water spokesman Jerry Grant said they will replace the connection with the public supply if it is made of lead, but the majority of the problem is the pipes within private homes.
The Cabinet is expected to sign off on a grant scheme to help low income families to replace affected pipes in their homes, while a public awareness campaign will also be launched.
Any pipe replacement scheme is likely to take years to complete, and comes after the Environment Protection Agency raised "serious concerns" in recent months about the risk of contamination from poorly-run waste water treatment facilities.
It is understood the problem was discovered by Irish Water and reported to Environment Minister Alan Kelly, who will brief his colleagues at their weekly meeting today.
Meanwhile, a consultation is being launched today on a range of proposals to divert water from the Shannon to supply the Dublin and eastern regions.
Some of the ideas up for discussion have faced opposition from community and environmental groups along the river.
Bord na Mona is backing one of the four options, to create a reservoir on the Laois-Offaly border using water from the Shannon.
Spokesman Colm Ó Gógáin thinks that plan will have minimal impact, saying the amount of water being considered is 4 cubic metres per second - compared to the Shannon's average flow of over 180 m3/s.
"The reality is the flows involved are less than 2% of the average flows of the Shannon," he said.
He also said that because of the way the technology works, the rate of flow would be decreased when the river's levels were low.