A question lands on your desk: an auditor wants to know why a sentinel temperature was logged at 48°C and what you did about it. Which document do you reach for? L8 tells you that you must have a scheme that controls the risk and acts on failures. HSG274 tells you what a sensible reading is and what to do when one drifts. You need both, and reaching for the wrong one first is how people tie themselves in knots.
So the difference is not academic. L8 and HSG274 answer different questions, carry different legal weight, and are built to be used in sequence. Confuse them and you can cite a temperature as if it were the law, or treat the law as if it came with a step-by-step method. It does neither.
The real decision: duty or method?
Every Legionella question you face is really one of two kinds. Some are duty questions — must I do this, who is accountable, what does “enough” look like in the eyes of the law. Some are method questions — what temperature, how often, which outlets, what to check after a refurbishment. L8 is built for the first kind. HSG274 is built for the second.
L8 is the Approved Code of Practice. That phrase is the whole point of it: a court can treat a failure to follow its relevant provisions as evidence that you breached the underlying health and safety law, unless you can show you controlled the risk an equally effective way [1]. HSG274 carries no such standing. It is technical guidance — a detailed, recognised account of how to actually do the controlling, published across parts that split by system type [2].
The pragmatic call is to stop asking “which one applies” as if it were either/or. On almost every site, both apply. The skill is knowing which one settles the question in front of you.
Side by side
Here is the comparison that matters once you stop treating them as one body of rules. The axes are the ones that change what you do, not just what you call the document.
| Decision axis | ACoP L8 | HSG274 (technical guidance) |
|---|---|---|
| What it is | Approved Code of Practice — the duty and management framework | Technical guidance — the recognised method |
| Legal standing | Special status: departure shifts the burden onto you in a prosecution [1] | No special status; a court can still weigh a departure from recognised guidance against you [1][2] |
| Question it answers | Must I, who is accountable, what counts as enough | How, what figure, how often, what to check |
| Typical content | Roles, written scheme, monitoring, records, review triggers | System schematics, sentinel outlets, temperatures, cleaning and inspection methods, sampling [2] |
| How it is organised | One management framework for any water system | Parts by system type: evaporative cooling; hot and cold water; other risk systems [2] |
| What citing it proves | That you had the right structure and accountability in place | That your method matched recognised good practice |
| When you reach for it | When defining duties, deviations, or “have we done enough” | When deciding or defending a temperature, interval or remedial action |
Read across any row and the split holds: L8 governs the shape of your compliance, HSG274 governs its content. Neither is sufficient alone. A faultless management framework wrapped around the wrong temperatures fails on method; a perfect flushing regime with no named responsible person and no review loop fails on duty.
Which one settles the question in front of you
Take the 48°C reading from the opening. L8 is what says you must have a written scheme that defines control limits, monitors against them, and escalates failures to a named person — and that you must keep the record [1]. HSG274 is what helps you judge that 48°C at a sentinel outlet is below the working expectation for hot water and warrants action, since stored hot water is commonly held around 60°C and expected to stay hot at the tap [3]. Treat that figure as the expectation your risk assessment confirms for your plant, not a number to defend regardless of what the system is doing.
So the answer to “which document” is: HSG274 to interpret the reading, L8 to prove you handled it properly. The auditor is really testing both at once — did you know what good looks like, and did you have the management chain to act on it.
That sequencing repeats across most questions:
- “How often should we sample?” — HSG274 and HSE guidance say frequency follows the system and the risk assessment, not a fixed calendar [4]. L8 is why you must record the reasoning.
- “Can we do it our own way?” — L8 is the document that grants and limits that freedom, through the equally-effective-alternative route [1]. HSG274 is the benchmark you would have to show your alternative matched.
- “Who carries the can if a contractor does the work?” — purely an L8 question. The duty holder keeps the legal duty whoever holds the spanner [1][5].
Where the confusion does real damage
The two get muddled in predictable, costly ways.
Citing HSG274 as if it were the law. A scheme that says “we comply with HSG274” and stops there has named the method but skipped the duty. The Code is the part that binds; the guidance is how you meet it. Lead with L8, support with HSG274.
Treating L8 as a manual. L8 will not tell you the inspection interval for a calorifier or how to clean a shower head. People who read it expecting that detail conclude it is vague. It is not vague — it is simply not the method document. The method lives in HSG274.
Assuming “L8 trained” means “knows the figures”. A provider fluent in the Code’s duties but hazy on the technical parts can build a tidy framework around weak method. The reverse — strong on temperatures, silent on accountability — is just as common.
Forgetting that one rooftop tower changes the map. Most commercial sites live in the hot-and-cold part of HSG274. A single cooling tower or evaporative condenser pulls a different part into scope and adds duties such as notification, on top of the same L8 framework [2][5]. The duty document does not change; the method document you need expands.
A note before you act on any of this
This is a general account of how the two documents relate, not a ruling on your building. The Code and the guidance are written to be applied through a competent, site-specific risk assessment — ideally to the BS 8580-1 standard — and the figures, intervals and remedial actions all turn on your system, who uses it and how [6]. Nothing here is legal advice or a substitute for reading the current published documents; where a duty or a number matters, confirm it against the source and a competent person rather than this page.
FAQ
When I write a control scheme, should I cite L8 or HSG274?
Both, and for different reasons. Cite L8 as the source of the duty your scheme discharges — the requirement to assess, control, monitor, record and review [1]. Cite HSG274 where you set or justify a method: temperatures, sentinel outlets, inspection intervals, cleaning [2]. A scheme that cites only one usually has a gap on the other. Documenting that split clearly is part of a defensible written scheme of control.
If HSG274 is only guidance, can we ignore it and do our own thing?
You can choose a different method, but you carry the cost of proving it. HSG274 is the recognised benchmark, so a departure from it can be weighed against you, and the only lawful route to “our own way” runs through L8’s equally-effective-alternative provision — which exists only if you can evidence the alternative achieved the same control [1][2]. In practice, follow the guidance and document any justified deviation.
Do I need to buy or read both documents?
Functionally yes, though they serve different shelves. L8 is the one you read to understand what you are accountable for; HSG274 is the one your responsible person and contractors work from day to day. A duty holder who has only read the guidance often knows the figures but not the legal exposure, which is the more expensive thing to get wrong.
Your next move
Open your current control scheme and read it with a two-colour pen: mark every duty statement (who, must, when to review) against L8, and every method statement (temperature, interval, outlet, action) against HSG274. Any sentence you cannot assign to one or the other is usually woolly, and any column that comes up thin is your real gap. If that scheme still lives in a binder where the duty and method are tangled together, mapping it into a digital logbook — one that ties each control limit to its trigger and its escalation — is the cleanest way to keep the two doing their separate jobs.
Sources
[1] HSE, “Legionnaires’ disease. The control of legionella bacteria in water systems - ACoP and guidance (L8)”. https://www.hse.gov.uk/pubns/books/l8.htm [2] HSE, “Legionnaires’ disease: Technical guidance (HSG274)”. https://www.hse.gov.uk/pubns/books/hsg274.htm [3] HSE, “Hot and cold water systems”. https://www.hse.gov.uk/legionnaires/hot-and-cold.htm [4] HSE, “Testing and monitoring your water system for legionella”. https://www.hse.gov.uk/legionnaires/testing-monitoring-water-system.htm [5] HSE, “Legionnaires’ disease - what you must do”. https://www.hse.gov.uk/legionnaires/what-you-must-do/index.htm [6] BSI, “BS 8580-1:2019 - Risk assessments for Legionella control. Code of practice”. https://knowledge.bsigroup.com/products/water-quality-risk-assessments-for-legionella-control-code-of-practice-1