A dozen dialysis patients have had their treatments cancelled after thieves stole a water meter from a health centre on Melbourne's outskirts.

The meter and a section of pipe were stolen from Melton Health, west of Melbourne, on Wednesday night, cutting water to the centre.

Melton Health chief executive Bruce Marshall said the facility was forced to cancel all appointments for its 12-bed renal dialysis unit on Thursday.

Dozens of appointments were also cancelled for the centre's dental unit.

"For dialysis patients, it's a significant issue," he told AAP.

Dialysis treatment is done every 48 hours and generally takes five hours.

Patient Wendy told ABC radio she was "gob-smacked" by the theft.

She said missing a treatment was serious.

"I'm rescheduled apparently for tomorrow and by then I'll be short of breath and have fluid build-up," she said.

"When I was there on Tuesday I had a full five-hour session, but there was one particular patient who was really sick on Tuesday, she never had a full session and so she'll really need a full session today."

Mr Marshall said he was confident the water would be back on by 4pm (AEDT) Thursday and the centre operating again on Friday.

But if it is not fixed, Mr Marshall said he had organised for patients to be treated at dialysis clinics in Sunbury and Williamstown on Friday.

The theft has been reported to police.

"I just seriously hope the person who has done this understands the implications of what they have done," he said.