Patients on two hospital wards have been banned from showering after the Legionella bacteria was found at Leicester General Hospital.
They have also been issued with bottled drinking water.
The measures were introduced on wards 28 and 29, used for surgical patients.
One patient, who asked not be to be named, questioned whether the hospital should admit patients while work to clear the bacteria – which can cause the potentially fatal Legionnaires' disease – was carried out.
But officials at Leicester's hospitals said patients were safe and the risk of Legionnaires' disease was low.
The patient said: "We were all given letters about the situation, given bottled water and told we couldn't shower or wash our faces for fear of Legionnaires' disease.
"We also had to use the bottled water for brushing our teeth and were given wipes for our face and hands."
The patient added: "I know the hospital is short of beds, however, I don't think you should open wards like this where many of the patients are elderly and quite frail.
"The doctors and nurses were fantastic, but I do think that having the wards open was putting patients at risk and of course the very words Legionella puts fear into people."
The disease is spread by small water droplets that evaporate very quickly from a contaminated water supply.
Legionnaires' disease is a severe pneumonia, an uncommon but serious illness, particularly for those who have weakened immune systems.
The presence of the bug was found during routine checks carried out on June 20. Restrictions are still in place while chlorine dioxide is added to the water supply to kill the bacteria.
Taps and showers are being regularly flushed and the water temperature checked as part of the cleansing process but officials are not yet sure when the system will be back to normal.
Dr David Jenkins, consultant medical microbiologist and deputy director of infection prevention and control at Leicester's hospitals, said: "Recent tests on wards 28 and 29 at Leicester General Hospital have triggered our safety plan, meaning showers on these wards will be out of use until further notice. Alternative body washing arrangements have been introduced.
"Bottled drinking water is also being provided for patients and staff but boiled drinks such as tea and coffee remain safe to drink."
He added: "We would like to reassure our patients that the risk of Legionnaires' disease for our patients remains low and they are safe.
"We would like to emphasise that the measures being taken are precautionary and there are no known cases of infection linked to this incident."
Dr Jenkins said the bacteria had been found in a routine safety check on water supplies.
He added: "Low levels of Legionella are not a cause for concern, however high levels can cause a form of pneumonia called Legionnaires' disease so we undertake routine testing to ensure the risk is kept low."
Legionnaires' disease is the result of legionella bacteria infecting a patient's lungs. It is usually caught by breathing in small droplets of contaminated water. It is not contagious and cannot be spread directly from person to person, according to the NHS Choices website.
Legionella bacteria is commonly found – usually at levels which are not harmful – in water sources such as rivers and lakes.
However, the bacteria can rapidly multiply if it finds its way into any artificial water supply systems or into air conditioning systems.