Written Scheme of Control: What It Is and Why Your Building Needs One
If you manage a building with a water system, you’ve probably come across the phrase “written scheme of control”. It’s a core part of Legionella control in the UK, and a surprisingly common gap in compliance. Here’s what it is, who needs one, and what it should contain.
What is a written scheme of control?
A written scheme of control (WSC) is a documented plan for how you manage the risk of Legionella bacteria in your water systems. It sets out what controls are in place, who is responsible for them, how often they’re checked, and what happens when something goes wrong.
It follows on from your Legionella risk assessment. The assessment identifies where the risks are, and the written scheme explains what you’re doing about them, day in and day out.
Why it matters
Legionella bacteria can cause Legionnaires’ disease, a serious and sometimes fatal form of pneumonia. The bacteria thrive in water between roughly 20°C and 45°C, especially where water stagnates and there’s scale, sludge or biofilm to feed on. They become dangerous when contaminated water is breathed in as fine droplets, for example from showers, spray taps or cooling towers.
In the UK, employers and people in control of premises, including landlords, have legal duties under the Health and Safety at Work etc. Act 1974 and the Control of Substances Hazardous to Health (COSHH) Regulations 2002. The HSE’s Approved Code of Practice L8 and guidance document HSG274 explain how to comply. Under that guidance, if your risk assessment shows a significant risk, you must prepare a written scheme for preventing or controlling it and then implement it. For a fuller overview, see our Legionella compliance guide.
Who needs one?
Any duty holder whose water systems present a reasonably foreseeable Legionella risk. That includes:
Workplaces, offices and factories
Hospitals, care homes and schools
Hotels, leisure centres and gyms
Any premises with cooling towers, evaporative condensers, spa pools or large hot and cold water systems
A small, simple system, such as a low-occupancy building with a small water heater and no stagnation risks, may need only a very simple scheme. But “low risk” still has to be justified and recorded.
What should it include?
A good written scheme is specific to your building. Typical contents are:
A description of the system. This means up-to-date schematic diagrams showing tanks, calorifiers, pipework, outlets and any “dead legs” (unused pipe runs where water sits still).
Responsible people. It should name the duty holder, the appointed responsible person and any deputies, along with their training and competence.
Control measures. These cover how you keep water at safe temperatures, avoid stagnation, keep systems clean and, where needed, use biocide treatment.
Monitoring and inspection routines. These include temperature monitoring, flushing of little-used outlets, shower head cleaning and descaling, and tank inspections, each with a stated frequency.
Temperature targets. HSG274 recommends storing hot water at 60°C or above, delivering it at 50°C or above within one minute at outlets, and keeping cold water below 20°C.
Sampling and testing. Where Legionella testing is needed, the scheme sets out when and how it will be done.
Remedial actions. It should say what you do when readings fall outside limits, for instance who is told, how quickly action is taken and how the problem is recorded and resolved. Where contamination is found, this may include disinfection and remedial works.
Record keeping. Logbooks and records should show that the scheme is actually being followed, and records are generally kept for at least five years.
Common mistakes
Treating it as a one-off document. A scheme that was written three years ago and never revisited is a liability.
Copying a generic template. Inspectors and, worse, outbreaks, don’t care about boilerplate. The scheme has to reflect your actual systems.
Writing it but not doing it. The paperwork is only worth something if the checks really happen and are recorded.
Forgetting changes. New pipework, a refurbishment, a change of use or a period of closure can all change your risk profile.
Unclear responsibility. If nobody knows who runs the temperature checks, nobody will.
Keeping it current
The scheme should be reviewed regularly, and whenever your risk assessment is reviewed. HSG274 suggests reviewing the risk assessment at least every two years, or sooner if there’s reason to think it’s no longer valid, such as changes to the water system, how it’s used or who uses the building, or a positive Legionella result. Many organisations choose to review the scheme annually as good practice. Our ongoing compliance support can take that burden off your team.
Final thoughts
A written scheme of control turns Legionella management from a vague intention into a clear, accountable routine. It protects the people who use your building, and it protects you by showing that you’ve taken reasonable steps to control the risk.
If you’re not confident in your current scheme, the team at Absolute Water Compliance can help. Get in touch to arrange a review, or find out more about our written scheme of control service.
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