A Duty Holder’s Guide to Legionella Control (ACoP L8)
What you must do to control legionella in water systems, set out in plain English from HSE’s ACoP L8 and HSG274.
What it is
The duty to control legionella comes from the Health and Safety at Work Act and COSHH. HSE’s Approved Code of Practice L8 and the HSG274 guidance set out how to manage the risk in hot and cold water systems, cooling towers and similar.
Who the duty holder is
The duty holder is the employer or person in control of the premises. They should appoint a competent "responsible person" to manage the control scheme day to day.
What it requires of you
- Identify and assess the risk of legionella across your water systems.
- Appoint a competent responsible person to take charge of the controls.
- Put in place and follow a written control scheme, including temperature monitoring, cleaning and disinfection.
- Monitor, inspect and keep records of the checks carried out.
- Review the risk assessment regularly and whenever the system or its use changes.
How often
| Sentinel outlet temperature checks | Typically monthly |
| Thermostatic mixing valves (TMVs) | At least annually |
| Risk assessment review | Regularly, and whenever circumstances change |
What happens if you don’t
Failing to control legionella breaches health and safety law and can lead to enforcement, prosecution and unlimited fines, alongside a real risk of serious or fatal illness.
Sources: Legionella (ACoP L8 and HSG274): HSE
This guide is general guidance, not legal advice, and is a summary only. Duties and intervals can change and depend on your circumstances. Always check the current regulation and take competent-person advice. Last reviewed June 2026.