ACoP L8 and HSG274: The Plain-English Guide to UK Legionella Compliance

You've been told you need to "comply with L8" — but nobody's explained what that actually means in plain English. ACoP L8 is the document that defines what UK duty holders must do about legionella. HSG274 tells you exactly how to do it. Together, they form the regulatory backbone of legionella water hygiene compliance in the UK.

This guide cuts through the jargon and explains both documents in terms a landlord, care home manager, or building owner can actually act on.

What ACoP L8 actually is

ACoP L8 stands for "Approved Code of Practice L8" — its full title is Legionnaires' disease: The control of legionella bacteria in water systems. It is published by the Health and Safety Executive (HSE).

An Approved Code of Practice has a specific legal status. It is not the law itself — the underlying law is the Health and Safety at Work etc. Act 1974 and the Control of Substances Hazardous to Health Regulations 2002 (COSHH). But if you are prosecuted and you did not follow ACoP L8, a court will assume you are at fault unless you can prove you complied another way.

In practice, ACoP L8 is the minimum standard every duty holder should meet.

The current edition was published in 2013 (fourth edition). It replaced an earlier version that included technical guidance — that detail now lives in HSG274.

What HSG274 is — the technical companion

HSG274 is the technical guidance that sits alongside ACoP L8. It is split into three parts:

Part 1: Evaporative cooling systems (cooling towers, evaporative condensers)
Part 2: Hot and cold water systems — this is the part relevant to most landlords, care homes, hotels, and offices
Part 3: Other risk systems (spa pools, humidifiers, water features)

For most duty holders reading this guide, Part 2 is the one that matters. It covers domestic-style hot and cold water systems — the type found in residential properties, care homes, dental practices, schools, and small commercial buildings.

HSG274 Part 1 was updated in 2024 (second edition) with improved guidance on evaporative cooling systems. Part 2 and Part 3 remain in their original editions — check the HSE website for the latest versions.

Who counts as a duty holder

ACoP L8 applies to anyone who is an employer or a person in control of premises where a water system is present. In practice, this means:

Residential landlords (including HMOs and single lets)
Care home managers and operators
Dental and GP practice managers
Hotel and B&B owners
School facilities managers
Commercial landlords (offices, retail units)
Employers with water systems in their premises

If you own or manage a building with a hot and cold water system, L8 applies to you. There is no exemption for small properties or low-risk buildings — the scope of your obligations may be simpler, but the obligation to assess and manage the risk still exists.

The seven things L8 requires you to do

ACoP L8 and HSG274 together require duty holders to maintain seven categories of compliance records. Here is what each one means in practice:

1. A current written legionella risk assessment

Every building with a water system needs a documented risk assessment. This identifies the hazards in your water system — dead legs, stored water temperatures, infrequently used outlets — and sets out the control measures needed.

HSE confirms that landlords of simple domestic systems can carry out their own risk assessment if they are competent to do so. More complex systems (cooling towers, large buildings) typically require a specialist.

2. Temperature monitoring logs

Hot and cold water temperatures must be checked and recorded regularly:

Check	Threshold	Frequency
Hot water at outlets	Must reach 50°C within one minute of running	Monthly (HSG274 Part 2, Table 2.1)
Hot water storage (calorifier)	Must be stored at 60°C or above	Monthly
Cold water at outlets	Must be below 20°C	Monthly
Sentinel outlets (nearest and furthest from source)	Same thresholds as above	Monthly

Legionella bacteria thrive between 20°C and 45°C. The temperature thresholds above keep water outside this danger zone.

3. Flushing records for infrequently used outlets

Any outlet not used for seven or more consecutive days must be flushed by running both hot and cold water. HSG274 Part 2 recommends flushing until the temperature at the outlet stabilises and is comparable to the supply water — typically at least two minutes for taps and showers.

This applies to guest rooms in hotels, vacant flats, seasonal facilities, unused taps in offices, and any outlet that sees irregular use. For detailed flushing guidance, see our guide to legionella flushing run times.

4. Quarterly showerhead and flexible hose cleaning

Showerheads and flexible hoses must be cleaned and descaled at least quarterly. These components create aerosols — the fine water droplets that carry legionella bacteria into the lungs — so they are a higher-risk part of the system.

5. TMV servicing records

Thermostatic mixing valves (TMVs) — the valves that blend hot and cold water to deliver safe temperatures at outlets — need regular servicing and functional testing. Frequency depends on the manufacturer's guidance, but annual servicing is typical.

6. Cooling tower and evaporative condenser records

If your building has a cooling tower or evaporative condenser, there are additional registration, testing, and record-keeping requirements under HSG274 Part 1. Most landlords and small building managers do not have these systems, but if you do, these requirements are significantly more onerous.

7. A documented written scheme of control

The written scheme of control is your compliance plan. It documents: what control measures are in place, who is responsible for each task, what the monitoring schedule is, and what to do if something goes wrong (for example, a temperature reading outside thresholds).

Think of it as the operating manual for your building's legionella control — it ties together the risk assessment, temperature monitoring, flushing, and cleaning into one document.

How L8 and HSG274 work together

ACoP L8 tells you what you must do. HSG274 tells you how to do it.

Document	Purpose	Legal status
ACoP L8	Sets out the duties of care and management requirements	Approved Code of Practice — quasi-legal force
HSG274 Part 2	Technical guidance on hot and cold water systems	Guidance — best practice, not legally binding on its own

In enforcement, HSE inspectors will check your compliance against both documents. Meeting L8 requirements using HSG274 methods is the most straightforward way to demonstrate compliance.

When to review your risk assessment

ACoP L8 requires risk assessments to be reviewed regularly. The 2013 edition removed the previous two-year fixed interval in favour of a risk-based approach. Reviews should happen:

At least every two years as a baseline (industry standard, even though L8 no longer specifies a fixed interval)
Immediately if the water system changes (refurbishment, new pipework, additional outlets)
Immediately if the building use changes (different occupants, change from residential to commercial)
After any significant event — extended building closure, positive legionella sample, near-miss

For higher-risk buildings (care homes, healthcare settings), annual reviews are appropriate. For a detailed breakdown of review intervals by building type, see our guide to risk assessment review frequency.

What happens if you do not comply

HSE continues to prioritise legionella compliance in its inspection activity. Local authority environmental health officers also have proactive enforcement powers.

The consequences of non-compliance range from improvement notices to criminal prosecution:

Improvement notice: requires you to fix the issue within a specified timeframe
Prohibition notice: requires you to shut down the water system until the risk is controlled
Criminal prosecution: fines and imprisonment under health and safety legislation, with penalties reflecting the severity of the breach

Legionella risk has been heightened in recent years by buildings that were closed or underused during extended shutdowns, leaving stagnant water in systems. This underscores why ongoing monitoring is essential.

Practical compliance summary

If you manage a building with a hot and cold water system, here is what you need to have in place:

Risk assessment — documented, current, reviewed at least every two years or after changes
Temperature logs — monthly hot (>50°C at outlets, >60°C stored) and cold (<20°C) readings recorded
Flushing schedule — weekly flushing of any outlet unused for seven or more days, records kept
Cleaning schedule — quarterly showerhead and hose descaling, records kept
TMV servicing — annual or per manufacturer's guidance, records kept
Written scheme of control — documented plan tying everything together
Responsible person — someone named as responsible for implementing the scheme

You do not need a "legionella certificate" — no such certificate exists in UK law. What you need are records that demonstrate ongoing compliance with the requirements above. For help creating a risk assessment document, see our guide to what a template should include.

Free tools to help

LegioLog offers free tools to help duty holders manage legionella compliance:

Legionella Risk Assessment Template Generator — generate a building-type-specific template
Temperature Compliance Checker — check readings against L8 thresholds instantly
Flushing Schedule Calculator — get a recommended flushing schedule for your building

This guide covers legionella compliance requirements under ACoP L8 and HSG274 for England, Wales, and Scotland. The same regulations apply across Great Britain. Northern Ireland has equivalent provisions under HSENI guidance. This is general compliance guidance, not legal or professional advice — for site-specific assessments, consult a competent person as defined by ACoP L8.