HMP Stoke Heath in Shropshire was left without water after supplies were affected for two days, the Prison Service has said.
Severn Trent worked to restore supplies after the issue started on Thursday - but no further information was given.
Inmates were given bottled water while the work was carried out.
A spokesman for the Ministry of Justice said the water supply to the jail was returned to normal at about 21:00 GMT on Friday.
The Category C prison near Market Drayton houses about 800 inmates.