Guidance · Reviewed September 2026
What happens after the risk assessment: the responsible person, the written scheme of control, the monitoring regime, what to do when a check or sample fails, and the records that prove the system is under control.
The short answer
Legionella control is not a one-off job. Where the risk assessment finds a foreseeable risk, ACoP L8 expects a named responsible person, a written scheme of control, routine monitoring at set frequencies, prompt remedial action when results fall outside the limits, and records kept for at least five years. Most enforcement cases are not about a missing risk assessment — they are about a scheme that existed on paper and was not being run.
The Five Parts of Legionella Control
1. Assess the risk
Identify and assess the sources of risk. Everything else is built on this.
2. Appoint a responsible person
Someone with the authority, competence and knowledge to manage the controls day to day, with a deputy to cover absence.
3. Run a written scheme
The plan that says what is checked, how often, what the limits are and what happens when they are missed.
4. Monitor and act
Carry out the checks, review the results and fix what they show. A reading outside the limit with no follow-up is evidence against you.
5. Keep records
Who is responsible, the assessment, the scheme, and the dated results of every check, inspection and test.
The first step has its own guide: see legionella risk assessment. For what the bacteria are and the conditions they need, see Legionella and Legionnaires’ disease. This page covers steps two to five.
The Responsible Person
The dutyholder — the employer, or the person in control of the premises — must appoint someone competent to take day-to-day responsibility for controlling the risk. That person needs sufficient authority to get things done, not just the job title: the power to stop an outlet being used, to call in a contractor and to spend money on remedial work. Appointing a deputy is sensible so that checks do not lapse during leave or sickness.
Using a water treatment contractor does not transfer the duty. The contractor carries out tasks; the dutyholder and the responsible person remain accountable for making sure those tasks are done, the results are reviewed and the actions are closed out.
What the Written Scheme Has to Contain
- an up-to-date plan or schematic of the system
- a description of how the system is meant to be operated correctly and safely
- the precautions to be taken to control the risk
- the checks to be carried out to confirm the precautions are working, and how often
- the remedial action to take if the scheme is shown not to be effective
It should name who does each task. A scheme that says “temperatures will be monitored monthly” without saying by whom is the kind that quietly stops being followed.
Control Methods
| Method | How it works | Where it fits |
|---|---|---|
| Temperature | Hot water stored at 60°C or above and delivered at 50°C or above (55°C in healthcare premises); cold water kept below 20°C. | The traditional and most common control for hot and cold water systems. |
| Avoiding stagnation | Removing dead legs and redundant pipework, and flushing outlets that are not used for seven days or more. | Every system, alongside whichever primary control is used. |
| Cleanliness | Inspecting and cleaning tanks and calorifiers, and descaling showers, spray taps and hoses. | Every system. Scale, sludge and biofilm feed the bacteria and shield them from heat and biocides. |
| Water treatment | Biocides and similar techniques such as chlorine dioxide or copper and silver ionisation, dosed and monitored to set levels. | Where the temperature regime cannot reliably be achieved, and as standard in cooling towers and spa pools. |
Whichever method is used, it needs its own monitoring. A dosing system that is installed and then left unchecked is not a control.
The Monitoring Regime for Hot and Cold Water Systems
| How often | What is checked |
|---|---|
| Weekly | Flush infrequently used outlets (anything not used for seven days or more), and keep a log once you start. |
| Monthly | Hot water at sentinel outlets (nearest, furthest and long branches): at least 50°C within one minute, 55°C in healthcare premises. Cold water at sentinel taps: below 20°C within two minutes. Calorifier flow (60°C) and return (not below 50°C) temperatures. |
| Quarterly | Dismantle, clean and descale showerheads, spray taps and hoses. Temperatures at the return legs of subordinate loops on circulating systems. |
| Annually | Inspect cold water storage tanks. Check tank and incoming mains temperatures, in summer. Inspect and clean calorifiers. Check thermal insulation. Inspect and clean the strainers on thermostatic mixing valves. |
These are the starting points in HSG274 Part 2, Table 2.1. The risk assessment may set different frequencies for your system, and those are the ones to follow. Healthcare and care settings usually need more frequent flushing and checks.
When a Check or a Sample Fails
An out-of-range temperature is a prompt to find the cause, not just a number to log. Common causes are a failed circulation pump, a thermostat set too low, poor insulation, cold pipes running alongside hot ones, or an outlet that is simply not being used.
If Legionella is found in a hot or cold water sample
More than 100 but fewer than 1,000 cfu per litre: if only one or two samples are positive, resample. If most samples are positive, the system may be colonised at a low level: review the control measures and the risk assessment, and consider disinfection.
1,000 cfu per litre or more: resample, and immediately review the control measures and the risk assessment to identify remedial action, including possible disinfection of the system.
These are the general action levels in HSG274 Part 2. In healthcare premises with susceptible patients, any detection should be investigated.
Cooling Towers, Spa Pools and Buildings Out of Use
Cooling towers and evaporative condensers need a full water treatment programme under HSG274 Part 1, with general microbiological monitoring weekly, Legionella sampling at least quarterly, and cleaning and disinfection at a frequency set by inspection and the risk assessment. They must also be notified to the local authority.
Spa pools and hot tubs, including display models, need continuous disinfection, regular water testing and their own sampling regime under HSG282.
Buildings or parts of buildings that fall out of use are a common source of problems. Either keep the weekly flushing going, or treat the system as shut down and clean, flush and where necessary disinfect it before it is brought back into use.
What Happens If Control Fails
HSE and local authorities investigate cases and outbreaks, and they prosecute. Breaches of the Health and Safety at Work etc. Act 1974 carry unlimited fines, individuals can be prosecuted as well as organisations, and where a gross failure leads to a death, manslaughter charges are possible. In practice the first documents an inspector asks for are the risk assessment, the written scheme and the monitoring records — and the gaps in those records usually tell the story.
Training
| If you need to… | Usual route |
|---|---|
| Act as the responsible person | Legionella Risk Management for the Responsible Person. |
| Hold the dutyholder role | Legionella Management for Duty Holders. |
| Carry out flushing and temperature checks | Legionella and Legionnaires’ Disease Awareness as a minimum, with site-specific instruction on your system. |
| Manage hot and cold water services in depth | BOHS P901 Management and Control of Building Hot and Cold Water Services. |
| Compare everything available | All legionella and water treatment courses. |
Frequently Asked Questions
Who can be the responsible person?
Anyone the dutyholder appoints who has the authority, competence, training and knowledge of the system to manage the controls. It is often a facilities or estates manager. It can be an external appointment, but the dutyholder stays accountable.
Can we do the monitoring in-house?
Yes. Flushing, temperature checks and showerhead cleaning are routinely done in-house by trained staff. Tank and calorifier inspections, disinfection and sampling are more often contracted out. Either way the results need to be reviewed by the responsible person, not just filed.
Does using a contractor mean the duty passes to them?
No. Contractors have their own duties for the work they do, but the dutyholder remains responsible for making sure the scheme is implemented and effective. Membership of the Legionella Control Association is a useful indicator when choosing one.
How long do we have to keep legionella records?
Records of monitoring, inspections, tests and checks should be kept for at least five years. The risk assessment, the written scheme and the details of who is responsible should be kept while they are current and for at least two years afterwards.
Does Envico provide legionella control services?
No. Envico is an independent training intermediary. This page is guidance, and the courses listed on it are delivered by independent training providers. Envico does not carry out or arrange risk assessments, sampling, disinfection or water treatment.
Related Guidance
General guidance only, reviewed September 2026 against the Health and Safety at Work etc. Act 1974, COSHH 2002, HSE’s Approved Code of Practice L8, HSG274 Parts 1 to 3 and HSG282. It is not a substitute for a site-specific risk assessment and written scheme prepared by a competent person. Envico is an independent training intermediary, does not carry out or arrange legionella risk assessments, sampling or water treatment, and is not affiliated with the HSE.