Legionella risk assessment: what’s actually required

UK-wide. The Health and Safety at Work etc. Act 1974 and the associated regulations apply across Great Britain, with equivalent provisions in Northern Ireland.

What the law actually says

The duty comes from general health and safety law — the Health and Safety at Work etc. Act 1974 and the Control of Substances Hazardous to Health Regulations — as applied to landlords by the Health and Safety Executive’s approved code of practice on legionella, usually referred to as L8.

The HSE’s own position on domestic lettings is unambiguous: landlords have a duty to assess and control the risk, the risk in most domestic systems is low, and a simple assessment carried out by a competent person is sufficient. It does not require testing, sampling, certification or a contractor.

Where the risk actually is

Legionella bacteria multiply between roughly 20°C and 45°C, in water that sits still, and infection happens by inhaling contaminated droplets — a shower spray, not a glass of water.

Feature	Risk	What to do
Combi boiler, no stored water	Very low	Record it. Water is heated on demand and not stored.
Hot water cylinder	Low, manageable	Ensure it stores at 60°C and distributes at 50°C or above at the taps
Cold water storage tank	Moderate	Check it is lidded, insulated, free of debris, and that cold water stays below 20°C
Showers	The main exposure route	Clean and descale the head and hose periodically
Infrequently used outlets	Moderate	An outside tap, a spare bathroom, a garden hose — flush them
Void periods	The real one	Flush all outlets before a new tenant moves in, especially after a long empty period
Thermostatic mixing valves	Moderate	Water sits at blended, ideal-growth temperatures. Check and service them.

Doing the assessment

1. Describe the system. Combi or cylinder, any cold water tank, number of bathrooms, any outlets used rarely, any thermostatic mixing valves.
2. Check temperatures. Hot water reaching about 50°C at the tap within a minute or so; cold below 20°C.
3. Look for dead legs — lengths of redundant pipework left behind after a bathroom was moved or a washing machine removed. Cap or remove them where practical.
4. Check any stored water is covered, insulated and clean.
5. Record what you found and what you did, with the date and your name. A single page is sufficient.
6. Review it when something changes — a new boiler, a new bathroom, a long void, a change of tenant — rather than on an arbitrary annual cycle.

What to tell the tenant

Include a short note in the tenant information you provide at the start of the tenancy:

• Do not adjust the boiler or cylinder thermostat below the setting provided.
• Flush unused outlets, including showers, if the property has been empty for a week or more.
• Clean and descale the shower head periodically.
• Report any problem with hot water temperature.

That note, plus your assessment, is a complete and defensible position for a normal domestic let.

When to bring in a professional

Genuinely higher-risk systems justify expert input: large or complex properties, communal water systems in blocks of flats, cooling towers or evaporative condensers, spa baths or hot tubs, sizeable HMOs with extensive pipework, or any property where you find you cannot answer the basic questions above. In a block of flats the communal system is the freeholder’s responsibility, and asking them for evidence of their assessment is the right step.

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