A leak at Llanfairpwll on Sunday morning affected supplies to some customers there and in parts of Gaerwen, Porthaethwy and Llangefni.
A spokesman said: "Our team is working on the leak and we hope that all supplies will be back to normal this morning."
Welsh Water apologised to customers for any inconvenience.
Parts of Anglesey have been left without water after a leak, Welsh Water has confirmed.