Irish Water and Donegal County Council are working to restore water supply to customers in the Glencolmcille and surrounding areas of south Donegal.
It follows reduced water output at Owentskna Water Treatment Plant and increased water demand in the area.
The reduced water output and increased demand were first noticed last Sunday.
The affected areas include Gleann Cholm Cille, Málainn Mór, Málainn Beag and surrounding areas.
Irish Water says it responded to the supply interruption, with crews working to reconfigure the network so as to restore supply to customers in Glencolmcille.
But works were again underway this morning to restore supply to areas affected.
Irish Water says residents and businesses may experience low water pressure or outages while reservoirs are being refilled.
Irish Water is also encouraging customers to conserve water while works are taking place.