Uisce Éireann says it is working to restore normal water supply to homes and businesses served by the Lough Mourne Public Water Supply Scheme.
An electrical issue has caused an unplanned plant shut down at the Meencrumlin Water Treatment Plant.
The utility says crews are on the ground working to restore supply as quickly as possible.
Homes in Ballybofey and Stranorlar, Glenfin, Liscooley Group Water Scheme, Rossgier to Porthall and Rossgier to Cavan Hill and customers served by the Tievebrack, Ballynacor and Gleneely/Lismullaghduff Reservoirs may experience reduced water pressure and/ or water outages today.
