Kerry Clarkson
Technical Lead
3rd February 2026
Q. What are the Legionella management responsibilities for an unoccupied building where water supply isolated? Should risk management plan be updated? e.g. No flushing, no temp monitoring etc.
A. This is generally covered under the mothballing section in HSG274. Where part of a building or a water system is taken out of use, Legionella and other microbial growth will need to be appropriately controlled. This is often a compromise between adequate control of microbial growth, the use of water for flushing (while avoiding waste) and degradation of the system by any disinfectant added. Generally, systems are normally left filled with water and not drained down as moisture will remain within the system enabling biofilm to develop. Any isolated systems will need to be recommissioned as though they were new (i.e. thoroughly flushed, cleaned and disinfected) before returned to use.
Q. When a Landlord with staff holding Duty holder/responsible persons responsibilities is using an FM provider as competent person(s), nobody is better placed to understand requirements to update written schemes than engineers on the ground, what would you suggest is best way for the management company to make sure that the written scheme is up to date and that all requirements are met?
A. If this is being done with minimal knowledge of the building or the water systems in place, then I would suggest cross referencing the findings of the Legionella risk assessment with the written scheme, then in turn checking that evidence is in place to demonstrate all the requirements of the written scheme are being implemented. There should be an annual review of the control measures, and this should also be checked as it could indicate changes to the building or water system that could mean the Legionella risk assessment is no longer valid. Following up on any remedial actions and out of parameter results is another good check as these things are often done but poorly documented.
Q. Where you have intermittent occupancy due to agile working, is there a recommend flushing regime to follow?
A. Flushing should always be done weekly as a minimum and include all high-risk outlets (showers and spray taps) regardless of usage, as well as any low use outlets. The duration should be proportional to the rough volume of water in the pipe from the source. i.e. if you know an outlet is at the end of a long run, then it should be flushed for longer.
If you do not have a means of knowing who is in and out of the building and the usage of the water systems, then you should consider all outlets in those areas to be infrequently used. Using a temperature probe during flushing will be the best way to confirm that the outlets have had sufficient turnover. Once the temperature at the outlet matches the incoming supply then the flush is complete, this could be 2 minutes or 12 minutes, depending on the building.
Q. I have my own water management regime in place, but as a tenant in a managed building, what questions should I be asking my building management team to ensure they are managing legionella properly?
A. There are a lot of duties under cooperation and coordination. Your landlord has a duty to carry out a Legionella risk assessment and make sure that there are suitable controls in place. The sharing of risk assessments is usually the first step in the process. Next would be asking for the written scheme, which should come off the back of the risk assessment. You can always request individual records to check this is being implemented, but these will usually be just a snapshot / the most recent results, especially if they use an online system where they will have to download records to show you. You could request water management be included to the agenda of your landlord tenant meetings (if not already discussed).
Q. Do you have any thoughts on managing outside bodies of water...buildings with ponds, fountains, waterfalls etc. Should we treat these the same as internal water?
A. These should be considered as part of your Legionella risk assessment and the requirements will vary off the back of that report, depending on the nature and complexity of the system. How big is the body of water and are parts of it likely to reach over 20oC in the summer months? Does it create a spray? Is there plant and animal life present? - this this could limit the controls that could be put in place. Is it located somewhere that potentially vulnerable people could be exposed to any splashing or droplets produced? These factors should all be considered, the risks calculated and a proportional regime put in place as needed.
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