What is a legionella written scheme of control?
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Key points
- The written scheme of control sets out how you will keep legionella risk under control in a named water system: the control measures, the checks, how often each is done, and who is responsible.
- It is a separate document from the risk assessment. The assessment identifies the risk; the scheme states what you will do about it.
- ACOP L8 requires a written scheme to be prepared and implemented once your assessment has identified a reasonably foreseeable risk.
- A usable scheme includes an up-to-date system schematic, the control parameters, monitoring tasks and frequencies, named responsibilities, and the action to take if control fails.
- It is a living document, reviewed whenever the system, its use, or the monitoring results change.
A written scheme of control is the document that sets out how you will keep legionella risk under control in a specific water system: the control measures you rely on, the checks you carry out, how often you carry them out, and who is responsible for each task. It is the practical answer to the question the risk assessment raises.
Under ACOP L8, once your risk assessment has identified a reasonably foreseeable risk, you are required to prepare a scheme for controlling that risk and then implement and manage it. The scheme is not a certificate and it does not, on its own, make a system safe. It is the standing set of instructions your monitoring and record keeping follow.
The assessment finds the risk; the scheme controls it
The two documents are often confused, and the confusion causes real gaps. A legionella risk assessment is a survey and a judgement. It maps the system, identifies where legionella could grow or spread, and rates the risk. Think of it as the diagnosis.
The written scheme of control is the treatment plan that follows. Where the assessment says "this calorifier runs below temperature" or "this outlet is little used", the scheme says what you will do about each finding, who will do it, and how you will know it is working. The assessment is a snapshot in time. The scheme is the ongoing regime for keeping the risk under control between assessments.
The risk assessment tells you where legionella could grow. The written scheme of control is your standing answer to the question: so what are you actually doing about it?
What the law actually requires
The duty sits under the Health and Safety at Work etc Act 1974, the Control of Substances Hazardous to Health Regulations, and the Management of Health and Safety at Work Regulations. The Approved Code of Practice and guidance, ACOP L8, is where the specific expectation to prepare a written scheme is set out, with the detail expanded in HSG274.
ACOP L8 does not prescribe a single template or a fixed length. What it expects is that the scheme is written down, is specific to your system rather than generic, and is actually put into practice. A scheme that sits in a folder and is never followed offers no control at all, and a court or inspector would treat it that way.
What a written scheme of control must contain
A scheme that will stand up to scrutiny, and that someone else could pick up and follow, generally covers the following.
- An up-to-date schematic of the system. A simple line diagram showing tanks, calorifiers, pumps, the pipework layout, and every outlet. If the drawing does not match the pipes, the scheme is already out of date.
- The control measures and their parameters. The specific values you are working to: hot water stored at 60°C and distributed so it reaches 50°C (55°C in healthcare) within one minute at the outlet, cold water kept below 20°C, and any secondary controls such as chlorine dioxide dosing. Legionella multiplies most readily between roughly 20°C to 45°C, which is why these figures matter.
- Monitoring tasks and their frequencies. What is checked, and how often. Monthly temperature checks at sentinel outlets, weekly flushing of little-used outlets, quarterly showerhead cleaning and descaling, annual calorifier inspection, and so on. A temperature chart and a log book give you somewhere to record each result.
- Who is responsible. The named responsible person (sometimes called the duty holder's appointed person) who manages the scheme, and the competent person or contractor who carries out or reviews the technical work. Responsibility should attach to a role and a name, not to "someone".
- What to do if control fails. The action to take when a check comes back out of range: a temperature below target, a positive sample, or a task missed. This is the part most generic schemes leave out, and it is the part that matters most on the day something goes wrong.
- Remedial action and escalation. How faults are logged, corrected, and signed off, and when you escalate to sampling or specialist help. Our guide on what to do if legionella is detected covers the response side in more detail.
The point running through all of this is specificity. A scheme that names your outlets, your temperatures, and your people is a working document. One that could apply to any building in the country is not.
Free legionella risk assessment template
A structured Word document following the five-step approach in ACOP L8. Covers risk identification, written scheme, monitoring, and records. If it isn't written down, you can't evidence it.
Follows ACoP L8 and HSG274 Part 2. Free. No spam.
It is a living document, not a one-off
A written scheme of control is never finished. It should be reviewed and, where needed, revised whenever something changes that could affect the risk: an alteration to the pipework, a change in how the building is used, a period of low or no occupancy, new plant, or a run of monitoring results that shows the controls are not holding. It should also be revisited if there is reason to believe it is no longer effective, for example after a positive sample or a suspected case.
Reviewing the risk assessment and the scheme together keeps the two in step. There is no fixed legal interval, but low occupancy, refurbishment, and any structural change to the system are all clear triggers to look again rather than wait.
Using the free template as a starting point
For a simple, low-risk premises, a hot and cold water system in a small office, a shop, or a modest let, a structured template gives you a sound starting framework: a place to record the schematic, the control parameters, the task list with frequencies, and the responsibilities. Our risk assessment template and log book are built to sit alongside a scheme in exactly this way.
A template records your decisions. It does not make them for you, and it does not replace competent judgement where the system is complex, serves vulnerable people, or includes higher-risk assets such as cooling towers or evaporative condensers. In those cases the scheme should be drawn up or reviewed by someone competent to do so. If you are unsure whether your premises even needs a full assessment first, see do I need a legionella risk assessment, and for what an external assessment might involve, the cost of a risk assessment.
How the scheme fits the wider guidance
Read the scheme as one part of a chain the HSE expects to see: identify who is responsible, assess the risk, prepare and put into effect a written scheme to control it, and keep records that show the scheme is being followed. That sequence is the backbone of ACOP L8 and is worked through in practical terms across the three parts of HSG274. Keeping your scheme current, specific, and evidenced through your records is how you demonstrate legionella compliance if you are ever asked to show it.
Free legionella risk assessment template
A structured Word document following the five-step approach in ACOP L8. Covers risk identification, written scheme, monitoring, and records. If it isn't written down, you can't evidence it.
Follows ACoP L8 and HSG274 Part 2. Free. No spam.
Frequently asked questions
What is the difference between a risk assessment and a written scheme of control?
The risk assessment identifies and rates the legionella risk: it surveys the system, maps where legionella could grow or spread, and records the findings. The written scheme of control is what you do about those findings: the control measures, the monitoring tasks, the frequencies, and the responsibilities.
Put simply, the assessment is the diagnosis and the scheme is the ongoing treatment plan. You need both, and ACOP L8 expects the scheme to follow once the assessment has identified a reasonably foreseeable risk.
Is a written scheme of control a legal requirement?
Yes, in effect. Where your risk assessment identifies a reasonably foreseeable risk, ACOP L8 requires you to prepare a scheme for controlling that risk and to implement and manage it. The underlying duties sit under the Health and Safety at Work etc Act, COSHH, and the Management of Health and Safety at Work Regulations.
Following the Approved Code of Practice is not the only way to comply, but if you do not follow it you must be able to show you have controlled the risk to an equivalent standard. A scheme that is written but never put into practice would not meet the requirement.
Who should prepare a written scheme of control?
Responsibility rests with the duty holder, usually the employer, landlord, or person in control of the premises, who must appoint a responsible person to manage it. That person needs to be competent, with enough knowledge, training, and authority to carry out the work.
For a simple, low-risk premises the responsible person may prepare the scheme themselves using a structured template. Where the system is complex, serves vulnerable people, or includes higher-risk plant such as cooling towers, the scheme should be drawn up or reviewed by someone with the relevant competence.
What should a written scheme of control include?
A workable scheme includes an up-to-date schematic of the system, the control measures and their parameters (such as hot water stored at 60°C and cold water below 20°C), the monitoring tasks and how often each is done, and who is responsible for each one. It should also set out what to do if a control fails and how remedial action is recorded and signed off.
The detail should be specific to your system rather than generic. A scheme that names your outlets, temperatures, and people is one that can actually be followed and evidenced through your records.
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