Patients have been moved from Penn Hospital in Wolverhampton after increased levels of Legionella bacteria was found in the water.
The trust says this is to ensure the comfort of patients is maintained, whilst urgent works take place.
It also confirmed all of the patients at the non-acute hospital had been transferred to other sites across the Black Country.
Chris Masikane, who is the Deputy Chief Executive and Chief Operating Officer, said: "Following routine water testing at Penn Hospital in Wolverhampton we can confirm that increased levels of Legionella bacteria has been identified in the water system."
What is the main cause of Legionella? And what is Legionnaires' disease?
Legionella is a bacterium that includes the species L. pneumophila, causing legionellosis including a pneumonia-type illness called Legionnaires' disease and a mild flu-like illness called Pontiac fever.
Most people catch Legionnaires' disease by inhaling the bacteria from water or soil.
According to the NHS, you can get Legionnaires' disease if you breathe in tiny droplets of water containing bacteria that causes the infection.
The NHS said: "It's usually caught in places like hotels, hospitals or offices where the bacteria have got into the water supply."
Older adults, smokers and people with weakened immune systems are particularly susceptible to Legionnaires' disease.
Mr Masikane adds: "To ensure the comfort of patients’ is maintained, we have temporarily moved them whilst urgent works takes place to rectify the problem.
"We are liaising with staff, families and carers to keep them informed.
"We want to reassure patients and the community that there are currently no confirmed cases, but we continue to monitor the situation closely."