In reply to J1234:
There's a brief mention of the Legionella risk in the BMC guidance. Before re-opening, it would be sensible for hot and cold water systems to be treated to reduce the risk of Legionnaries' disease. The highest risk comes from showers (and taps with diffusers). All systems will differ but the following would be sensible and not over the top. Systems that rely on private water supplies, water off the hill, etc or that have header tanks on the cold side will need more careful thought / treatment. To be done before any other use of systems:
1) Run a hot tap to drain until at least the volume of the system including storage tanks has been flushed through. Select a tap with the least potential for causing an airborne water mist and keep out of the way whilst running. (Wearing a FFP3 respirator would be sensible if there's a chance of inhaling water droplets at this stage).
2) Remove shower heads and hoses (and tap diffusers if possible) and soak them in a bucket of 1:40 household bleach solution, disassembling shower heads as much as possible to make sure disinfectant gets into all the nooks and crannies.
2) Turn on water heaters and ensure they are turned up to 70 degC. Allow to reach full temperature right through the tank (feel the bottom) and leave for at least an hour to give heat time to kill off bacteria.
3) Go round each hot water outlet in turn and run carefully, without splashing or burning yourself, for a few minutes. This will allow thermal disinfection of the pipe run and outlet. Wait for heater to get back up to temperature before going to next outlet.
4) Flush each cold outlet in turn for a minute or two to make sure there's no old water left in there.
5) Disinfect taps and surrounding area preferably using bleach solution (but be careful not to kill off the waste water tank bacteria by putting bleach down the drain if the hut isn't on mains sewers).
6) Re-assemble showers, etc and run through with hot water then cold water, direct to drain.
7) It would be good to keep the hot water system operating at 65 to 70 degC, at least for the first week or two of use, but ensure that users are made aware of the risk of scalding. (It should never be turned down such that hot water comes out of the furthest tap at less than 50 degC.)