Almost 8,700 Irish Water customers connected to the Newmarket Regional Water Supply are being asked to boil their water before use until further notice.
The utility company say they cannot guarantee that drinking water has been disinfected properly due to Storm Barra.
Homes and businesses in Newmarket, Kanturk, Ballydesmond, Boherbue and the surrounding areas are impacted by the issue.
Meanwhile customers in Carrigtwohill, Blarney, Tower, Whiddy Island and Drinagh may experience some supply disruption due to burst mains and power outages.
Customers in the Eyeries and Ardgroom areas will also be without water due to power disruption at the Glenbeg Water Treatment Plant.
