Legionella & Water Hygiene · 8 min read

Updated 28 May 2026

ACOP L8 and HSG274 Explained (Plain English)

Q: What is ACOP L8?

ACOP L8 is the Approved Code of Practice and guidance for "Legionnaires' disease: the control of Legionella bacteria in water systems". It sits under the Health and Safety at Work Act and COSHH, and has special legal status — courts can use it to judge whether a duty holder acted reasonably.

Q: What is HSG274?

HSG274 is the technical guidance published by HSE that sits alongside ACOP L8. It comes in three parts: Part 1 covers evaporative cooling systems (cooling towers); Part 2 covers hot and cold water systems; Part 3 covers other risk systems like spa pools, vehicle wash, humidifiers and dental water lines.

Q: Is ACOP L8 the law?

Not in itself — the underlying law is HSWA 1974, COSHH 2002 and the Management of H&S at Work Regulations 1999. But L8 has "approved" status: if you follow it, you are likely to comply with the law; if you don't follow it, you must show you've done something at least as effective.

Q: Who does L8 / HSG274 apply to?

Anyone with a duty under HSWA — employers, landlords, the self-employed and people in control of premises — where the work activity, water system or use of premises could present a risk of exposure to Legionella.

Pipe Assassin Technical Team — G3 certified, WRAS approved — 10+ years in UK plumbing & water hygiene

ACOP L8 is the Approved Code of Practice on Legionella, sitting under the Health and Safety at Work Act. HSG274 Parts 1-3 are the practical HSE guidance that goes with it: Part 1 for evaporative cooling (cooling towers), Part 2 for hot and cold water systems, Part 3 for other risk systems. If you're a duty holder, these are the documents you and your contractor are working from.

ACOP L8 — what it is

Full title: "Legionnaires' disease: The control of legionella bacteria in water systems — Approved Code of Practice and guidance" (4th edition). It applies to every undertaking involving a work activity, premises, or water system in which Legionella could be a risk.

"Approved" status

ACOP documents have a special status under the HSWA. If you follow L8, a court or inspector will normally take that as evidence of compliance. If you choose to do something different, you must show you achieved the same level of protection. In practice, following L8 is the cheapest route.

L8 sets out the duties:

Identify and assess sources of risk.
Prepare a scheme of control.
Implement, manage and monitor the control measures.
Keep records.
Appoint a competent "responsible person" with the authority and resources to manage it.

HSG274 — the practical detail

Where L8 says what you must do, HSG274 says how. It's split into three parts so duty holders can use the one that matches their system:

Part	Covers	Who needs it
Part 1	Evaporative cooling systems — cooling towers and evaporative condensers	Any building with a notifiable cooling tower or evaporative condenser
Part 2	Hot and cold water systems — calorifiers, cylinders, tanks, distribution, outlets, TMVs	Everyone with a building water system — domestic let, commercial, healthcare
Part 3	Other risk systems — spa pools, vehicle wash, humidifiers, dental unit waterlines, fountains, fire systems	Operators of any of these systems

HSG274 Part 2 — the one most people need

For UK homes, lets, offices, schools and care homes, Part 2 is the practical bible. It spells out the temperature regime that most readers of this site will be working to:

Stored cold water < 20°C; reaching that within 2 minutes of running at sentinel outlets.
Stored hot water ≥ 60°C in the calorifier.
Hot water distribution ≥ 50°C (≥ 55°C for healthcare) within 1 minute at sentinel outlets.
Monthly sentinel temperature checks; annual checks of representative outlets on subordinate loops; monthly calorifier flow/return.
Annual cold water storage tank inspection; clean as conditions require.
Quarterly / six-monthly TMV servicing depending on setting and risk.

The full temperature picture is in our 20/50/60 rule guide; the pillar is safe hot water temperatures.

L8 / HSG274 compliant water hygiene work — written, recorded, reviewed

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Parts 1 and 3 — the specialist ones

Part 1 covers evaporative cooling. If you've got a cooling tower or evaporative condenser, you must notify HSE (Notification of Cooling Towers regs 1992) and operate to a specific written scheme. These are higher-risk systems with the potential for community-scale outbreaks; the regime is more involved than for hot & cold water systems.

Part 3 covers a grab-bag of other risk systems — spa pools, hot tubs, decorative water features with fine sprays, humidifiers and air-washers, vehicle washes and dental water lines. Each has its own routine.

How a duty holder actually uses these documents

1
Get a copy
L8 and HSG274 are published by HSE. PDFs are available; for healthcare and complex sites, buy the printed copies.
2
Cross-reference with your risk assessment
Your assessment should reference the L8 duties and the relevant HSG274 part — not just be a generic form.
3
Build the scheme of control from HSG274
Use the recommended monitoring schedules as the starting point; adjust to your specific system.
4
Train your responsible person
They need to understand the documents enough to know what to ask the contractor and what records to keep.
5
Review when guidance changes
HSG274 has been updated several times; check you're working from the current edition.

Ninja Tip

If your contractor can't tell you which paragraph of HSG274 Pt2 their monitoring schedule is based on, that's a flag. A real water hygiene job is L8/HSG274 by the page — not by guesswork. See the wider picture in the Legionella control pillar guide or look at landlord-specific duties in landlord responsibilities.

Frequently Asked Questions

What is ACOP L8?

ACOP L8 is the Approved Code of Practice and guidance for "Legionnaires' disease: the control of Legionella bacteria in water systems". It sits under the Health and Safety at Work Act and COSHH, and has special legal status — courts can use it to judge whether a duty holder acted reasonably.

What is HSG274?

HSG274 is the technical guidance published by HSE that sits alongside ACOP L8. It comes in three parts: Part 1 covers evaporative cooling systems (cooling towers); Part 2 covers hot and cold water systems; Part 3 covers other risk systems like spa pools, vehicle wash, humidifiers and dental water lines.

Is ACOP L8 the law?

Not in itself — the underlying law is HSWA 1974, COSHH 2002 and the Management of H&S at Work Regulations 1999. But L8 has "approved" status: if you follow it, you are likely to comply with the law; if you don't follow it, you must show you've done something at least as effective.

Who does L8 / HSG274 apply to?

Anyone with a duty under HSWA — employers, landlords, the self-employed and people in control of premises — where the work activity, water system or use of premises could present a risk of exposure to Legionella.

Sources & further reading

Guidance only. This article is general information for UK readers, not a substitute for a site-specific assessment by a competent person. Regulations and best practice change — always check the current official guidance and, for compliance work (Legionella risk, unvented cylinders, water regulations), use a suitably qualified professional. Pipe Assassin is an electric-boiler and water-hygiene specialist and is not Gas Safe registered; we do not carry out gas work.

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