ACOP L8 and HSG274: The Legionella Duty Explained (2026)

Legionella bacteria can grow in almost any water system, and if they are breathed in as a fine spray they can cause Legionnaires’ disease, a potentially fatal form of pneumonia. If you run a business or manage a building with a water system, controlling that risk is a legal duty. This guide explains the two documents at the heart of legionella compliance, ACOP L8 and HSG274, and what they mean for you in practical terms.

Where the legal duty comes from

The duty to control legionella flows from general health and safety law: the Health and Safety at Work etc. Act 1974 and the Control of Substances Hazardous to Health Regulations 2002 (COSHH). Legionella bacteria are a “substance hazardous to health”, so the ordinary COSHH duty to assess and control the risk applies.

What is ACOP L8?

ACOP L8 is the Approved Code of Practice titled “Legionnaires’ disease: The control of legionella bacteria in water systems”, published by the HSE. An Approved Code of Practice has a special legal status. You do not have to follow it to the letter, but if you are prosecuted for a breach and you have not followed it, you must show that you complied with the law in some other equally effective way. In practice, ACOP L8 is the benchmark against which your arrangements will be judged.

L8 sets out the duties on the “dutyholder”, the employer or whoever is in control of the premises, to identify and assess the risk, prepare a scheme to prevent or control it, appoint a competent “responsible person” to manage it, keep records, and review the arrangements.

What is HSG274?

If ACOP L8 tells you what you must achieve, HSG274 tells you how. It is the detailed technical guidance that sits underneath L8, published in three parts:

• Part 1, evaporative cooling systems (cooling towers and evaporative condensers);
• Part 2, hot and cold water systems (the part that applies to most ordinary buildings);
• Part 3, other risk systems, such as spa pools, humidifiers and vehicle washes.

HSG274 Part 2 is the one most businesses and landlords will rely on. It covers practical control measures: keeping hot water hot (stored at 60°C and distributed so it reaches taps at 50°C), keeping cold water cold (below 20°C), removing “dead legs” of little-used pipework, and flushing infrequently used outlets.

What you actually have to do

Boiled down, a compliant approach looks like this:

• Carry out a legionella risk assessment of your water system, and review it regularly or whenever the system changes;
• Appoint a competent responsible person to take day-to-day charge of managing the risk;
• Put a written control scheme in place, covering temperature monitoring, flushing regimes, tank inspections and so on;
• Keep records of monitoring and remedial work;
• Review everything when circumstances change.

You can read more about what this involves and what it typically costs in our guide to legionella risk assessment costs.

Specialist settings: healthcare, spa pools and swimming pools

Some environments carry extra requirements on top of L8 and HSG274. Healthcare premises follow HTM 04-01 (“Safe water in healthcare premises”), which also addresses Pseudomonas aeruginosa in augmented-care settings. Spa pools and hot tubs are covered by HSG282, and swimming pools by HSG179. If you operate any of these, the general legionella duty still applies, and the specialist guidance sits on top of it.

What about landlords?

This is an area where there is a lot of misinformation, much of it pushed by companies selling “legionella certificates”. Here is the accurate position. Landlords do have a legal duty to consider and, where necessary, control the risk of legionella in the properties they let, because the same health and safety law applies. However, for most ordinary domestic rented properties the risk is low, a simple assessment is usually enough, and the landlord can carry it out themselves. There is no legal requirement to hold a “legionella certificate”, to have testing or water sampling carried out, or to pay a contractor for a routine domestic let. The picture changes for larger or more complex situations, such as HMOs, blocks with communal or stored water systems, or purpose-built student accommodation, where a more thorough professional assessment is genuinely warranted.

Frequently asked questions

Is ACOP L8 a law?

It is an Approved Code of Practice, which has a special legal status. The underlying legal duties come from the Health and Safety at Work Act and COSHH. L8 is the recognised way of demonstrating you have met them.

How often should a legionella risk assessment be reviewed?

Regularly, and always when there is reason to believe it is no longer valid, for example after changes to the water system, the building’s use, or the people using it. Two years is a common review interval for lower-risk systems.

Do landlords need a legionella certificate?

No. There is no such legal requirement. Landlords must assess and manage the risk, but for most domestic lets that is a simple, proportionate exercise, not a paid certificate or water test.

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