Irish Water says lead problems in the water system have been ongoing for years, but were dealt with at local level until now.
Home owners in Dublin have become the first to receive letters from the utility warning them that their supply may be contaminated with unsafe levels of lead.
Around 26,000 homes around the country will be sent similar letters in the coming weeks.
Jerry Grant, head of Asset Management at Irish Water, says the issue of lead in the water is not new, they have just collated the information on a national level for the first time.
He said: "If you go back over the EPA reports for the last 15 years, you'll see indications in those reports of lead problems from place to place.
"The difficulty was that individual local authorities, and there were 34 of them, were dealing with this in an ad hoc basis, so from time to time lead problems would arise and they would be dealt with locally between the local authority and the HSE.
"Obviously, when we took over responsibility from January 2014, we began to collate all that information and pick up more detail around the extent of lead piping around the system."
Mr Grant also said they have funding to eliminate lead from the whole public system, but they will also prioritise homes where upgrade have been done.
He said: "We will be doing it on a priority basis where we have identified the risk, but when any householder decides to replace the lead in their property, if they contact us, we undertake to immediately replace the public side on their properties.
"Right now in Limerick we recently signed a contract to complete all public-side lead in Limerick city.
"We will be continuing that anyway as part of our normal programme, but specifically when a householder commits to replace the lead within the property, we undertake on notification to replace on our side as well, so that that house at least is clear."