Residents have been warned that water in some houses in Galway city has been found to contain high levels of lead.
Galway City Council and the Health Service Executive West said the lead was found during recent tests of houses in Old Mervue, Shantalla, Bohermore and the Claddagh areas of the city, where lead piping is still installed in many properties built before 1970.
They warned people living and working in the Old Mervue area not to drink the tap water, which was worst affected by the lead contamination. It said arrangements were being made to provide a supply of drinking water for people in the area.
The council insisted that water leaving its treatment works "does not contain lead and is of a very high quality".
However, it said part or all of the service pipes connecting the water main in the street to the kitchen tap in older buildings may be made of lead, which can build up in the body and serious harm to young children and unborn babies in particular.
Over-exposure to lead can damage the nervous and reproductive systems and kidneys, and can cause high blood pressure and anaemia. At very high levels, lead poisoning can cause convulsions, coma and death.
Boiling water does not remove lead.
Further sampling of the drinking water in Galway City is being conducted to investigate the extent of the problem, the council said.
It is the second incidence of serious water contamination in Galway City in the past 18 months.
Last year, over 90,000 people in Galway city and county were forced to boil water due to contamination caused by the cryptosporidium parasite.