The Horizon Health Network in New Brunswick says St. Joseph's Hospital also closed its urgent care centre and has been diverting patients to the Saint John Regional Hospital.
Brenda Kinney, executive director of Saint John Regional Hospital, says staff from St. Joseph's transferred to her facility for the day and took in additional patients.
Kinney says the day started with a boil order due to a water main break, and the hospital lost water pressure and was unable to operate some of its facilities.
She says St. Joseph's continued to operate its diagnostic services during the day.
She says the city has informed the hospital the water main is repaired and it's expected St. Joseph's will reopen all services Wednesday.
The city says about 45,000 customers were affected by the boil order, which will remain in place until two consecutive tests done 24 hours apart show the water is safe to drink.
The boil order applies to areas east of the Reversing Falls Bridge.