Legionella Control: 4 Checks Facilities Managers Can Assign Today
Effective legionella control rests on three things: keeping water out of the growth range, with cold below 20°C, hot storage at 60°C or above and distribution at 50°C or above (55°C in healthcare); a written control scheme run by a competent person; and preventing stagnation through flushing and removing deadlegs. HSE sets these temperatures. Records prove the regime is working.
TL;DR:
Check storage and sentinel outlets monthly, rotate other points according to system complexity, and keep monitoring records for at least five years.
Use microbiological sampling to verify controls after remedial work or when risk assessment warrants it; routine testing is not required for most enclosed systems.
A competent person needs authority and installation specific knowledge, while dutyholders retain responsibility; employers with five or more staff must record significant findings and actions.
Where assessments identify scalding risks, fit thermostatic mixing valves at affected outlets, keep outlet runs short, and include valve maintenance in the written scheme.
Flush rarely used outlets at a frequency set by the risk assessment, descale shower heads quarterly, clean cold water tanks annually, and remove redundant pipework.
Table of Contents
What should you check and assign today?
Start with a short list you can hand to staff or a contractor. Each item needs a named owner and a date.
Check hot storage and sentinel outlet temperatures every month, and log the readings against the targets.
Flush unused outlets regularly, and increase the frequency where your risk assessment says to.
Write down who the responsible person is and where the written control scheme is kept, so an auditor or an out-of-hours engineer can find both.
Agree the escalation route in advance: isolate affected outlets, investigate system faults, arrange disinfection or remedial works, and log every action taken.
If a reading fails and nobody knows who to call, the list has not done its job. Fix that gap first.
How does temperature control act as your primary defence?
Temperature is the main lever because Legionella multiplies in lukewarm water. The targets are fixed: cold water below 20°C, hot water stored at 60°C or above, and hot water reaching outlets at 50°C or above (55°C in healthcare premises) within one minute, per HSE’s healthcare guidance.
Cold below 20°C. Hot storage 60°C or above. Distribution 50°C or above, 55°C in healthcare, within one minute. These are the benchmarks every temperature check is measured against.
Choose your sentinel points deliberately. Use the outlets nearest to and furthest from the storage plant, then rotate through representative other outlets so that, over time, you build a temperature profile of the whole system. On complex systems, scale the number and frequency of checks to match. Our guide on completing temperature monitoring checks shows how to select and record them.
When a value falls outside target:
Look for deadlegs, redundant pipework and faulty circulation first.
Re-test to confirm the reading before acting on it.
Escalate to the competent person, and record the failure and the fix.
Which routines keep systems clean and moving?
Stagnation can encourage bacterial growth, so routine tasks matter alongside temperature. HSE’s practical measures include avoiding water between 20°C and 45°C, flushing unused outlets regularly, descaling shower heads quarterly and cleaning cold-water storage tanks at least annually.
Flush infrequently used outlets regularly, and more often where the risk assessment requires.
Inspect cold-water tanks, check that lids fit and vents are screened, and insulate where heat gain from nearby plant is a risk.
Remove redundant pipework and shorten long runs to outlets, because HSG274 design guidance calls for removing redundant pipework and keeping water moving.
Favour materials that do not encourage microbial growth when you replace components.
Pro Tip: Walk the building with the schematic and look for outlets nobody remembers using. Rarely used spare bathrooms and old sinks are classic stagnation points, and a flushing rota that skips them gives false comfort.
What should you monitor, and how long do you keep the records?
Temperature checks are your core monitoring: monthly on storage, monthly at sentinel outlets, and rotational checks of other points, with frequency scaled to system complexity. Where disinfectants are used, follow the monitoring regime set out in the written scheme.
Microbiological sampling plays a different role. HSE describes it as a verification tool, not a substitute for effective operational controls, and routine testing is not required for most enclosed hot and cold systems unless the regime is ineffective or temperatures cannot be maintained. Use it after remedial works or when the risk assessment points to it, and have a competent person interpret the results. Our guide to interpreting Legionella water samples explains what the numbers mean.
Dutyholders with five or more employees must record significant findings and the steps taken, according to HSE’s record-keeping guidance.
Keep monitoring, inspection, test and check records for at least five years.
Keep the risk assessment and written scheme while current, and for at least two years afterwards.
Who is the competent person, and what goes in the written scheme?
HSE requires a competent person with sufficient authority, skills and knowledge of the specific installation. Responsibility stays with the dutyholder even when contractors do the work. Our explainer on the responsible person for legionella covers how to document the appointment.
Where a reasonably foreseeable risk exists, ACOP L8 expects a written scheme. See also what UK dutyholders must have in a written scheme.
A system schematic and operating instructions.
The control measures, monitoring points and frequencies.
Remedial actions and named responsibilities.
Include review arrangements in the written scheme, based on the risk assessment.
When do you need thermostatic mixing valves?
Hot water high enough to control Legionella can scald, so the two risks must be balanced. Where a scalding risk is identified, such as vulnerable users or whole-body immersion, HSE’s guidance calls for thermostatic mixing valves (TMVs) at the relevant outlets, and for measuring the hot inlet temperature to each valve.
Fit TMVs where the assessment shows a significant scalding risk.
Keep the run between valve and outlet short to help avoid water stagnation.
Include TMV maintenance in the written control scheme.
Put the scalding assessment inside the risk assessment and record the approach you chose.
When should you add thermal or chemical disinfection?
Disinfection supplements, and does not replace, temperature control and flushing. Thermal and chemical disinfection may be used as remedial measures or as part of a treatment programme, following assessment by a competent person.
Copper–silver ionisation and chlorine dioxide can work, but need proper installation, dosing and competent oversight.
Any biocide must sit within the written scheme.
Record monitoring data in line with the written scheme.
Where dosing is continuous in a large system, combine it with regular flushing, as HSG274 advises.
Is automated temperature monitoring worth adopting?
It can be. Remote systems allow more frequent temperature checks and help identify infrequently used outlets. HSG274 technical guidance says they should rest on a site-specific risk assessment agreed by a competent person. Treat them as verification, plan who reviews alerts and what happens next, and decide sensor placement and data handling so the output feeds the written scheme.
Why a control scheme only works if it fits the site
Many failures are not missing documents but generic ones. A scheme copied from another building misses the deadleg behind a refurbished bathroom or the ward that now houses more vulnerable people. Tailoring wins, and so does acting fast when a check fails. We tailor schemes and monitoring to each site’s systems and occupants, investigate failures and support records and audits. Training and automated monitoring help dutyholders meet their obligations.
— Sammi
How can we help you put this in place?
We deliver and maintain the controls described above:
Legionella risk assessments, from £185
Water testing and analysis, from £55 per sample
TMV servicing, tank cleaning, disinfection and ongoing maintenance contracts
[
Request a bespoke quote or arrange a site visit and we will map these measures onto your site.
FAQ
How long should you run a tap to prevent Legionella?
HSE guidance centres on regular flushing of unused outlets rather than a single run time. Regular flushing is a sensible baseline, and your risk assessment should set the duration and frequency for each outlet. HSE lists regular flushing among its core practical measures.
What disinfectant kills Legionella?
Thermal and chemical disinfection are both used, typically as remedial measures after contamination or within a treatment programme. Copper–silver ionisation and chlorine dioxide are examples. Whatever is used must be dosed and monitored under competent oversight and recorded in the written scheme.
Can wearing a mask prevent Legionella?
A mask is not a substitute for controlling Legionella in the water system. Focus on temperature control, flushing, cleaning and monitoring. Dutyholders should focus on the measures above.
What are the legal requirements for controlling Legionella risks in the UK?
Dutyholders must assess the risk and, where a reasonably foreseeable risk exists, run a written scheme under a competent person, as set out in ACOP L8. Those with five or more employees must record significant findings and the steps taken.
Recommended
Comments