Test have confirmed a high level of lead in water supplies in more than half of the houses surveyed in Galway city.
The report by the Health Service Executive shows that four areas of the city have contaminated water supplies.
Houses in the areas of Old Mervue, Bóthar Mór, The Claddagh and Shantalla are affected.
The issue prompted an emergency meeting of Galway City Council tonight.
Mayor of Galway Cllr Padraig Conneely said he had been contacted by City Manager Joe McGrath concerning lead related problems in older pipes in pre-1970's houses.
The HSe has advised that boiling water does not remove lead and says that it can build up in the body and cause harm, particularly in young children and unborn babies.
It says that further sampling of the drinking water in Galway City is being carried out to find the extent of the problem.
People living in the affected houses in the city are being contacted to offer repeat water testing and to arrange for clinical follow-up.
This latest development follows Galway's cryptosporidium outbreak in March 2007 when 240 people fell seriously ill and thousands more reported feeling unwell.
A boil water notice remained in place for five months.
Galway water supplies were declared safe in August of last year.
The outbreak was the most serious of its kind in this country and led to major political rows over failure to replace the old treatment plant at Terryland before the emergency arose.
