Four Manchester hospitals cancelled operations on Monday morning after a burst water main hit supplies.
Patients have been urged not to attend the Manchester Royal Infirmary, Manchester Royal Eye Hospital, Saint Mary's Hospital and Royal Manchester Children's Hospital while the problem is rectified unless there is an "urgent clinical need".
Manchester University NHS Foundation Trust said cancer operations would take place as planned, along with any urgent procedures.
The trust said it was contacting patients and that operations would be rescheduled "as soon as possible".
All outpatient services will be running as usual on Monday and anyone with an appointment has been told to attend it as planned.