One of the most common issues I come across when carrying out Legionella risk assessments is surprisingly simple:
There is no written scheme of control in place.
The site may have:
- A recent risk assessment
- Some temperature checks
- Occasional monitoring
…but no clear, structured plan explaining how Legionella risk is actually being managed.
And that’s a problem.
What Is a Written Scheme of Control?
A written scheme of control is a site-specific document that sets out how you manage and control the risk of Legionella within your water systems.
It should clearly define:
- What control measures are required
- Who is responsible for each task
- How often tasks are carried out
- What the acceptable limits are (e.g. temperatures)
- What to do if something goes wrong
In simple terms — it’s your plan for staying compliant and keeping people safe.
Why Is It So Important?
Without a written scheme, there is:
- No clear structure
- No accountability
- No consistency
This often leads to:
- Tasks being missed
- Monitoring being inconsistent
- Confusion over responsibilities
- Increased risk within the system
From a compliance point of view, it also means you are not meeting UK guidance under ACOP L8 and HSG274.
What I Commonly See on Site
In reality, this is what it usually looks like:
- “We’ve got a risk assessment somewhere…”
- “Our contractor does the monitoring”
- “We flush outlets when we remember”
But when you ask for the written scheme — it doesn’t exist.
Or it’s:
- Generic
- Outdated
- Not relevant to the actual system
A written scheme should never be a copy-and-paste document — it needs to reflect your specific building and water systems.
What Should Be Included?
A suitable written scheme of control should cover:
System Overview
A clear description of your water systems, including:
- Cold water storage
- Hot water systems
- Outlets and usage
Control Measures
For example:
- Temperature monitoring
- Flushing of infrequently used outlets
- Cleaning and disinfection
- TMV servicing
- Tank inspections
Responsibilities
Who is responsible for:
- Day-to-day tasks
- Monitoring
- Oversight
- Reviewing the system
Monitoring & Frequency
How often tasks are carried out, such as:
- Weekly flushing
- Monthly temperature checks
- Quarterly inspections
Action Levels
What constitutes a failure, and what action is required:
- Hot water below 50°C
- Cold water above 20°C
- Poor flow or stagnation
Records
What needs to be recorded and retained:
- Temperature logs
- Flushing records
- Maintenance reports
The Risk of Not Having One
Without a written scheme of control, you’re relying on:
- Memory
- Assumptions
- Inconsistent processes
This is where things start to go wrong.
In the event of:
- A failed audit
- An incident
- Or worse — a case of Legionnaires’ disease
…the lack of a written scheme becomes a serious compliance issue.
It’s Not Just Paperwork
A good written scheme isn’t just a document — it’s a practical tool.
The sites that manage Legionella well are the ones where:
- Everyone knows what needs to be done
- Tasks are clearly assigned
- Monitoring is consistent
- Issues are picked up early
That all starts with having a clear, usable scheme in place.
Final Thoughts
If you have a Legionella risk assessment but no written scheme of control, there’s a gap in your compliance.
It doesn’t need to be complicated — but it does need to be:
- Clear
- Site-specific
- Actively used
If you’re unsure whether your current setup meets requirements, it’s worth reviewing before it becomes a bigger issue.
Need Support?
At Edge Water Hygiene, we help businesses put together practical, easy-to-follow written schemes of control that actually work on site — not just on paper.
If you need help reviewing or creating a written scheme, get in touch.
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