Stagnant/stale water will probably be found in your pipes and storage systems.
You MUST NOT put a property back into use without first considering the water quality, as during this period of inactivity the water systems will have stagnated, or, if systems have been drained down there may be pockets of water that remained in the system.
During the lockdown period and after, The Health and Safety at Work etc Act still applies and as such Duty Holders must take all reasonably practicable steps to control the risk from legionella (and other waterborne pathogens) throughout this time.
We have been advised that the HSE is unlikely to treat this COVID-19 lockdown as any exemption to the Duty Holder being prosecuted should it be shown their actions [or lack of] caused a case/s or outbreak.
For each property / water system, a recommissioning plan should be detailed. The number of steps in this plan will vary depending on the complexity and size of the water systems and importantly on the people who will be using these systems, this includes those undertaking the recommissioning works.