Thames Water said 26,000 properties in Reading and Wokingham were affected when a pump at Earley failed.
The company said the fault occurred at about 06:30 BST and supplies and pressure were restored at 16:00.
At least three schools - Hillside Primary, White Knights and Leighton Park School - closed as a result of the problems.
Thames Water apologised for any inconvenience caused and said its engineers brought in water from other areas of Berkshire to supply customers in Reading.
The company warned that water may be discoloured when it first came back.
It said it was "harmless" but advised customers to keep taps running until it cleared, and to inform the firm if it continued.
Free bottled water depots had been set up in the car parks of the University of Reading, Asda at Lower Earley and Showcase Cinema at Winnersh for those affected.
Thousands of people in Berkshire were left without water or low pressure following a pump failure.