Guernsey's Princess Elizabeth Hospital will have its water system flushed with chlorine after Legionella bacteria was detected in the water supply.
The cleansing of the system will take place over two Sundays, 15 and 22 January, during which time taps and toilets will be unavailable.
Bottled water and portable toilets have been provided as alternatives, and the hospital restaurant has been closed.
The Legionella bacteria was found in the water supply in early January 2012.
The Health and Social Services Department announced that while the level of bacteria was higher than acceptable, it stressed that no patients or staff had been taken ill with associated illnesses.
Prior to flushing out the system, water storage tanks and pipes were drained and cleaned.
Chlorinated water will be flushed through the pipework of the hospital's new clinical block, the Divette Ward, De Sausmarez Ward, Pathology, the Children's Dental Unit, Housekeeping, the former Sherwill Ward and staff accommodation at John Henry Court later.
The remainder of the hospital will be treated on 22 January.