A damaged water pipe at St Albans City Hospital meant some patients were diverted to other units on Saturday.
The hospital was alerted to the low water pressure at 8am, and began an immediate investigation and remedial works.
The pipe was repaired and back in action by 11am.
Mariane Covington, spokesperson for the hospital, said: "We would like to apologise for the delays experienced by a small number of patients who were affected by the damaged water pipe supplying part of our site at St Albans Hospital including our dialysis unit on Saturday.
"In the interim, water was supplied to the unit by an existing storage tank, with some patients diverted to other units in order to minimise delays."