Limerick County Council has issued its second boil water notice this week after the bacteria E.coli was found in the Pallasgreen water supply.
Earlier this week, the local authority issued a similar public alert to over 153 domestic and non-domestic customers of the Rockhill public water supply.
In a statement, the council said "continued extensive testing" by environmental laboratory staff had since identified the problem in the Pallasgreen supply also.
A total of 100 households are affected, in areas including Knockanea, Grange West, Knockeen, Ballyart, Castle-Erkin, Woodfarm, Dromkeen, Drombane, Sunville, Garranemore, Dromlara, Lisheen, Ballyvoneen, Brackylea and Linfield.
Director of services Paul Crowe said: "The introduction of a boil notice is deemed a necessary precautionary measure to ensure that public health is not put at risk."
Water supplies have been monitored for safety after recent heavy rainfall. Boil notices are also in place in Sligo, for areas served by the Killsallagh supply. Meath County Council lifted a boil notice for Moynalty and Athboy yesterday.
In areas where a boil notice is in place, any water for drinking purposes, brushing teeth and food preparation should be boiled first.