Those effected are in the areas of Bundoran Town and environs, Loughside (Co. Leitrim), Rathmore, Ballymuntirhiggin, Lisahully, Clyhore and surrounding areas.
Some of those effected may still be effected by pressure issues.
Irish Water says that following heavy rain over the last 36 hours, water levels at Lough Melvin have risen to a critical level and have caused serious flooding at the Bundoran Water Treatment Plant, Co. Donegal.
Last night the ESB had to disconnect mains power to the treatment plant due to water levels rising to within 12mm of the electrical control panels.
2 Fire Brigade Units spent the night pumping water out of the buildings and levels have reduced.
Water was shut off to all supply areas at midnight last night to conserve supply. The supply has since been returned, but some houses may be experiencing low pressure.
Electricians are on site at the moment, trying to get the plant restarted and running on generator power.
Irish Water has apologised for the inconvenience and say they are working hard to resolve the issue as soon as they can.