Reducing the risk
Prior to reoccupation the initial review should focus on whether the water systems have remained in regular use or a manual weekly flushing regime has been implemented consistently to simulate use. A flushing regime should include all outlets to ensure turnover of water within the system is achieved. All outlets should be flushed until the temperature at the outlet has stabilised.
If the water systems on site have been reliably flushed each week then consideration should be given to undertaking some validation sampling to confirm water quality in the system is acceptable prior to reoccupation.
If sufficient turnover has not been maintained through occupation or manual flushing then additional remedial work will be necessary to ensure the safe recommissioning of the water systems. The most appropriate course of action will depend on the size, design and complexity of the water system in a building but would typically require a cleansing flush at maximum velocity followed by validation sampling as a minimum. A full system clean and disinfection may also be necessary.
It is important that records of all actions taken to ensure the safety of the water systems and good quality of the water within it are correctly filed for future reference and scrutiny and to demonstrate that those responsible for Legionella control in the building have fulfilled their legal obligations.