Uisce Éireann has said it may take some time before full water services are restored everywhere.
More than 130,000 people are without water and and the company last night warned that supplies for a further 750,000 people were at risk.
Head of Water Operations at Uisce Éireann, Margaret Attridge, warned that service disruptions may last a number of days for some households and businesses.
“This was an unprecedented storm event that has had a severe impact on our water and wastewater network nationwide," she said.
"We are still assessing the full extent of the disruption to supplies. Our crews will work around the clock where it is safe to do so to restore water service as quickly as possible, but given the extent of the damage, it may take some time before full service is restored everywhere.
"We ask for the public’s continued patience during this challenging time.”
Power outages at treatment plants and pumping stations continue to impact on supplies across the county.
Once power is returned to an area, Uisce Éireann said it may take some time for normal water supply to be restored.
Customers can go to water.ie and enter their address for details of localised issues and estimated restoration times. Details of alternative water supplies if required will also be provided here.
Repair crews have commenced restoration works and are coordinating with the National Emergency Co-ordination Group, local authorities, the ESB, Civil Defence and other agencies to restore normal supplies as quickly as possible.
In the meantime, customers are urged to conserve water where possible in order to protect supply while the outages are resolved.