A third of Alderney residents will be without water while repairs are carried out to a major leak.
States engineer Julie Turner said the supply would be shut off from 2000 BST on Thursday until 0200 BST on Friday.
She said: "This is unavoidable and will allow the water board to fix a major leak close to the Trigale tank.
"I apologise for the disruption that this will cause, and advise that you plan to store water for minor use during this period."
The work is expected to affect the Mouriaux, western parts of Allee es Fees, lower Petit Val, Church Street, La Vallee, Braye Road, Newtown, Crabby including hospital, fire station and power station, Platte Saline, Picaterre, Lower Rd, Banquage, the lower part of Valongis and Braye Street.
The five-strong team at the Water Board have responsibility for supplying 1,300 households and commercial users on the island.
The water supply is generated from a number of streams and bore holes and stored at the Battery Quarry and Corblets Quarry.