More prisoners have been moved at Magilligan Prison in Co Derry after Legionnaires' Disease was discovered.
Health experts are treating the contaminated supply and reviewing the entire water system at the jail.
Legionella Bacterium was discovered in the water at the healthcare centre of the jail after a dying inmate tested positive in hospital in Coleraine last week.
The prison governor said this evening he did not think the prisoner's death was related to Legionnaire's disease. It is a lung infection which produces flu-like symptoms.
There is no evidence to suggest the bacteria is present anywhere else in the prison, but prisoners are being moved out of the special supervision unit which shares the health centre's water. Six inmates had already been relocated.
The move followed a meeting today between representatives of the prison, the Western Health and Social Services Board and the Health and Safety Executive for Northern Ireland.
As a precaution, water samples will be taken from the other ten water systems within the centre.
There are 420 prisoners at the facility, which opened in 1972 on the site of a British army camp.
It is to be replaced with a £150m prison with up to 1,000 cells to house high-risk offenders.
