HSG274: A Complete Guide to the HSE’s Legionella Technical Guidance
Last updated: May 2026 | Reviewed by H2O Comply
If you are responsible for a building or its water systems, you have almost certainly come across HSG274. It is the technical guidance the Health and Safety Executive expects you to follow when controlling the risk of Legionella, and the standard against which your compliance will be judged if anything ever goes wrong.
This guide explains what HSG274 is, the three parts it is split into, who it applies to, and the practical duties it places on you. It also covers the 2024 update to Part 1.
If you would rather skip the reading and get expert help meeting your obligations, our Legionella compliance team works with duty holders across Kent, London, Essex, Surrey, Sussex and the wider southeast. Talk to the team.
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What is HSG274?
HSG274 is the Health and Safety Executive’s technical guidance document, titled Legionnaires’ disease: Technical guidance. It sits alongside the Approved Code of Practice known as ACoP L8 and provides the practical detail behind it.
Put simply, ACoP L8 tells you what the law expects. HSG274 tells you how to actually do it. Where L8 sets out the legal framework for controlling Legionella bacteria in water systems, HSG274 gives the technical advice on temperatures, monitoring regimes, inspection frequencies, and control measures that make compliance achievable in practice.
It is worth being clear on one point that causes a lot of confusion: HSG274 is guidance, not law in itself. But it gives practical advice on meeting the legal requirements of the Health and Safety at Work etc Act 1974 and the Control of Substances Hazardous to Health Regulations 2002. In practice, following HSG274 is how you demonstrate you have met those legal duties, and failing to follow it is how you end up exposed if there is an incident or an inspection.
The HSG724 Guidelines: The three parts of HSG274
HSG274 is divided into three parts, each covering a different type of water system. Most duty holders are affected by at least one, and many by all three.
HSG274 Part 1: Evaporative cooling systems
Part 1 covers cooling towers and evaporative condensers. If you operate or are responsible for any type of evaporative cooling system, this is the part that applies to you.
These systems carry a high Legionella risk because they generate fine water droplets that can travel considerable distances, which is why Part 1 is the most prescriptive of the three. It was updated in 2024 (more on that below), making it the most current part of the guidance.
Typical duty holders here include manufacturers, data centres, large commercial buildings with cooling towers, and industrial sites. Cooling towers are also notifiable to the local authority, a requirement that is easy to overlook.
HSG274 Part 2: Hot and cold water systems
Part 2 covers hot and cold water systems, and it is the part that applies to the widest range of premises by far. Almost every commercial building has a hot and cold water system, which means almost every duty holder needs to understand Part 2.
It is also the part where most organisations get caught out. The guidance covers water temperatures (keeping hot water hot and cold water cold), regular flushing of infrequently used outlets, monitoring and record keeping, and the management of tanks, calorifiers, and pipework.
Because these systems are so common, Part 2 is where the bulk of day-to-day Legionella management happens. If you are unsure whether your current controls are adequate, a Legionella risk assessment is the starting point.
Whatever your premises, if you are unsure whether your current controls meet Part 2, a Legionella risk assessment is the starting point.
HSG274 Part 3: Other risk systems
Part 3 covers everything else that can create a Legionella risk, including spa pools, decorative water features, humidifiers, vehicle washes, and similar systems that generate aerosols.
This is the part most often left out of risk assessments, usually because the systems involved are seen as minor or decorative. They are not. A poorly maintained water feature in a reception area can present a genuine risk.
Note that spa pools have their own dedicated guidance, HSG282, which sits alongside Part 3 and provides more detailed advice for those systems specifically.
Who does HSG274 apply to?
HSG274 applies to duty holders. In the language of the guidance, a duty holder is an employer, a person in control of premises, or anyone with health and safety responsibilities for others.
In practice, that covers a very wide range of people and organisations:
- Employers responsible for a workplace
- Building owners and landlords
- Facilities and building managers
- Anyone in control of premises where water systems are used
The sectors that most commonly need to act on HSG274 include care homes, hospitals and healthcare premises, schools and universities, hotels and hospitality, offices and commercial buildings, gyms and leisure centres, dental practices, and manufacturing and industrial sites.
If you are unsure whether the guidance applies to your premises, the safe assumption is that it does. Almost every building with a water system falls within its scope.
Your legal duties under HSG274
There are five core duties for duty holders. Understanding these is the foundation of compliance.
Most duty holders work with a specialist to meet these obligations, particularly the risk assessment and ongoing monitoring. Speak to our Legionella compliance team if you would like support.
HSG274 and the law
It is worth restating the legal position clearly, because it is widely misunderstood.
HSG274 is technical guidance. It is not, in itself, a piece of legislation. However, it is the standard the HSE and the courts use to judge whether you have complied with your actual legal duties under the Health and Safety at Work etc Act 1974 and the COSHH Regulations 2002.
This means that in practice, following HSG274 is how you stay on the right side of the law. If there is a Legionella incident, an outbreak, or an inspection, the authorities will look for evidence that you followed the guidance. Failing to do so can result in improvement notices, prohibition notices, and in serious cases, prosecution with significant fines.
What HSG274 compliance looks like in practice
Meeting your duties under HSG274 comes down to a handful of practical activities.
Legionella risk assessment. The starting point for everything. A competent assessor reviews your water systems, identifies risks, and recommends control measures. This should be reviewed regularly and whenever your systems or building change. Learn more about our Legionella risk assessments.
Written control scheme. A documented plan setting out the control measures for your specific systems, who is responsible, and how each measure will be carried out.
Monitoring and testing. Ongoing checks, such as temperature monitoring, flushing of little-used outlets, and water sampling where appropriate, are carried out at the frequencies the guidance recommends.
Record keeping. Detailed, dated records of every check, test, and remedial action. These are your proof of compliance and the first thing an inspector will ask for.
Training and competence. Your responsible person and anyone carrying out water hygiene tasks must be adequately trained and competent for the role.
Common HSG274 compliance mistakes
In our experience, the same gaps come up again and again. The most common mistakes include:
- Treating the risk assessment as a one-off rather than a living document that needs regular review
- Failing to update the assessment after building works, occupancy changes, or system alterations
- Incomplete or missing temperature monitoring records
- Overlooking Part 3 systems, such as water features and humidifiers
- Appointing a responsible person who has not been properly trained
- No evidence of management review or oversight
Most of these are easy to put right once identified, but they are exactly the gaps that cause problems during an inspection or after an incident.
The 2024 HSG274 Part 1 update
In 2024, the HSE published an updated version of HSG274 Part 1, the part covering evaporative cooling systems. It was the first significant revision since the guidance was first published in 2014, and importantly, the HSE updated only Part 1, not Parts 2 or 3.
The key changes include more prescriptive recommendations on inspection tasks and their frequency, new guidance on keeping photographic records before and after cleaning, and clarified wording around record keeping for small organisations.
If you operate any kind of evaporative cooling system, you should review your current practices against the 2024 version of Part 1 to make sure your controls and records still meet the updated expectations.
Frequently asked questions
Is HSG274 a legal requirement?
HSG274 is guidance rather than law, but it sets out how to meet your legal duties under the Health and Safety at Work etc Act 1974 and COSHH 2002. Following it is how you demonstrate compliance, so in practical terms it is not optional.
What is the difference between HSG274 and ACoP L8?
ACoP L8 is the Approved Code of Practice that sets out the legal framework for Legionella control. HSG274 is the technical guidance that explains how to put L8 into practice. They work together.
How often should an HSG274 risk assessment be reviewed?
A risk assessment should be reviewed regularly, typically at least every two years, and whenever there is a significant change to your water systems, building, or occupancy. Some higher-risk systems need more frequent review.
Who can carry out an HSG274 risk assessment?
A competent person with adequate training and experience. Many duty holders use an external specialist registered with the Legionella Control Association to ensure the assessment is robust and defensible.
What happens if I do not comply with HSG274?
You risk improvement or prohibition notices from the HSE, and in serious cases prosecution and substantial fines. More importantly, you risk a Legionella outbreak that could harm people.
Where can I download HSG274?
HSG274 is published by the HSE and is available to download for free from the HSE website. The three parts are available as separate PDFs.
Has HSG274 been updated?
Yes. Part 1, covering evaporative cooling systems, was updated in 2024. Parts 2 and 3 remain as previously published.
Getting help with HSG274 compliance
Understanding HSG274 is one thing. Meeting every duty it places on you, across every water system in your building, and keeping the records to prove it, is another.
At H2O Comply, we help duty holders meet their HSG274 and ACoP L8 obligations, from risk assessment through to ongoing monitoring and compliance.
Whether you need a first Legionella risk assessment, a compliance review of your existing controls, or ongoing water hygiene management, we can help.
Talk to our team about HSG274 compliance or call 0800 689 3463
Get expert help with HSG274 compliance
With over 15 years’ experience in water hygiene and Legionella control, H2O Comply helps businesses, landlords and property managers meet their HSG274 and ACoP L8 obligations. Our assessments and reports are UKAS accredited, City and Guilds trained, and LCA, HSE and CQC compliant.
Whether you need a first Legionella risk assessment, a review of your existing controls, or ongoing water hygiene management, we can help. Covering Kent, London, Essex, Surrey, Sussex and Hampshire.
