ACOP L8 is the document that tells you what controlling Legionella actually means in a workplace. It is short, it is free to read, and a surprising number of duty holders have never opened it — usually because they assumed it was a technical manual for water engineers rather than a statement of what the law expects of them.
This article explains what it is, the legal weight it carries, who it applies to, and the five duties it sets out.
What ACOP L8 is
L8 — Legionnaires' disease: The control of legionella bacteria in water systems is an Approved Code of Practice published by the Health and Safety Executive. It provides a framework for controlling exposure, gives advice on the Health and Safety at Work etc. Act 1974 and the COSHH Regulations, and covers the management, selection, training and competence of the people involved.
The legal status is the part that matters
An Approved Code of Practice is not ordinary guidance. It has a specific standing: if you are prosecuted for a breach of health and safety law, and it is proved that you did not follow the relevant provisions of the ACOP, a court will find you at fault unless you can show that you complied with the law in some other, equally effective way.
That is a meaningful difference from a best-practice document. You can depart from an ACOP, but the burden shifts to you to demonstrate that what you did instead was at least as good.
Who it applies to
ACOP L8 is aimed at duty holders. In practice that means employers, people in control of premises, and anyone with health and safety responsibilities for others. If you run a business from a building, manage a building on someone else's behalf, or are the responsible person for a premises where people work or visit, it applies to you.
It is worth being precise about the boundary here, because it is where most confusion sits. A landlord letting a single house is covered by the general duty in section 3 of the Health and Safety at Work Act, and the HSE says most such landlords can assess the risk themselves. An employer, or a person in control of commercial premises, is squarely within the ACOP's scope and is expected to work to it. We set out the residential position separately here.
The five duties
Stripped to its essentials, the ACOP requires a duty holder to do five things:
- Identify and assess sources of risk. Know what water systems you have, where water is stored, where it can stagnate, where aerosols are created, and who could be exposed.
- Prepare a scheme to prevent or control the risk. A written plan setting out the measures — temperature regimes, flushing, cleaning, treatment — that will actually keep the risk down.
- Implement, manage and monitor the precautions. Doing it, not just writing it. This is where most schemes fail, because the plan exists and the monitoring quietly stops.
- Keep records of the precautions. Dated evidence that the scheme was followed.
- Appoint a manager responsible for others. A named person who owns the scheme, with the authority and competence to run it.
Notice that four of the five are about management rather than plumbing. A duty holder with a good assessment and no monitoring regime is not compliant.
Temperature control — the numbers
Where temperature is used as the control method, the figures are specific:
- Hot water storage: at least 60°C.
- Hot water at the outlet: at least 50°C within one minute of running — 55°C in healthcare premises.
- Cold water: below 20°C, in storage and at the outlet.
Everything between those two thresholds is the range in which Legionella multiplies. The whole of temperature control is the discipline of keeping water out of that band.
Monitoring frequencies
The practical regime for hot and cold water systems runs roughly as follows:
- Sentinel outlet temperatures — monthly.
- Cold water storage temperatures — every six months.
- Shower heads — dismantle, clean and descale quarterly, or as the risk assessment determines.
- Infrequently used outlets — flush weekly.
- Storage tanks — inspect condition and lids; keep stored volume to around a day's usage; link multiple tanks so water flows through each rather than stagnating.
- Dead legs — remove dead ends and blind ends where possible; flush what remains.
HSG274 — the technical detail
Where the ACOP tells you what is required, HSG274 tells you how. It is published in three parts: evaporative cooling systems; hot and cold water systems; and other risk systems such as spa pools and humidifiers. Most commercial duty holders live in Part 2. If your premises has a cooling tower or an evaporative condenser you are in Part 1 territory, and there is also a separate legal duty to notify the local authority that the device exists.
Where duty holders most often fall short
- The assessment exists; the scheme does not. A risk assessment identifies hazards. A written control scheme says what will be done about them, by whom and how often. The ACOP requires both.
- Monitoring started and stopped. Six months of temperature readings followed by two years of silence is worse than none, because it demonstrates that you knew what was required.
- No named responsible person. Or a name belonging to someone who left.
- Nothing was reviewed after a change. A refurbishment, a new tenant, a floor taken out of use, an extension — each changes the water system, and each should trigger a review.
- Records that cannot be produced. If you cannot find them, they do not help you.
What to do with this
If you are an employer or in control of commercial premises, read the ACOP itself — it is free and it is not long. Then check whether you have all five elements: an assessment, a written scheme, active monitoring, records, and a named person. Most organisations that come to us have the first and the last, and a gap in the middle three.
That gap is what we are usually asked to close, and it is closed with a schedule and a logbook rather than with equipment.