A burst water main which affected supplies to about 2,500 customers in the east of Cardiff has been repaired, says Dwr Cymru Welsh Water.
Customers in Llanrumney and Rumney were affected but a spokesman said supplies should now be returning to normal.
Rumney High School has been closed, while tankers are at St Illtyds and Llanrumney High Schools and bottled water was being supplied to some .
Welsh Water has apologised for the inconvenience.
It is expected Rumney High will reopen on Thursday and all pupils were making their way to Eastern Leisure Centre, where they will be supervised until collected by parents.
Some customers may notice a slight discoloration to their tap water as supplies start to return. The spokesperson said this is normal and should clear within a short period.
If anyone has concerns about their water, they should call the operational helpline on 0800 052 0130.