Legionella Risk Assessment: What It Is and Who Needs One

A Legionella risk assessment is a written, site-specific assessment of a water system and the risks it poses to anyone exposed to it. It is a legal requirement under the Health and Safety at Work Act and COSHH for anyone in control of non-domestic premises (and for landlords of rented property). It is not a "certificate" — there is no such legal document.

What a risk assessment actually contains

A suitable and sufficient Legionella risk assessment, in line with ACOP L8, includes:

• A description of the water system, ideally with an up-to-date schematic.
• An identification of any potential sources of risk — cold tanks, calorifiers, showers, TMVs, dead legs, infrequently used outlets, spray taps, cooling towers, spa pools, etc.
• An assessment of who could be harmed and how, with attention to vulnerable users (older people, immunocompromised, very young).
• The existing controls — temperatures, cleaning regimes, flushing, monitoring.
• Recommended remedial actions, prioritised.
• A written scheme of control: who does what, when, and how it's recorded.
• A review date.

Who needs one

The landlord "Legionella certificate" myth

This needs spelling out, because tenants and landlords are still being mis-sold packages. There is no legal "Legionella certificate" for a rented home. The HSE says so directly. What the law actually requires of a landlord is a competent, written risk assessment — and for an ordinary single-let domestic property with combi heating and no stored water, that assessment is short and the controls are simple: stored hot at 60°C, cold below 20°C, flush rarely-used outlets, tell tenants to do the same in periods of low use, check it again when something changes.

How often to review it

The legal test is "review whenever there is reason to suspect it is no longer valid". Triggers include:

• Changes to the water system (new pipework, new appliances, removal of a tank).
• Change of use of the building or change in user group (e.g. tenants now include vulnerable people).
• Periods when the building has been left empty or partially empty for prolonged periods — see empty properties.
• A case of Legionnaires' disease linked or potentially linked to the premises.
• New guidance or new evidence that the controls aren't working.

As a routine, most water hygiene contractors review:

Who can do a risk assessment

A "competent person" — someone with adequate training, knowledge, experience and access to the right information. For a simple domestic rental, a landlord who has read HSE landlord guidance and is genuinely confident in the system can do their own. For anything with stored water, calorifiers, TMVs, showers in let property, HMOs, or larger premises — use a competent water hygiene contractor.

For deeper detail on a landlord's overall position, see landlord responsibilities. For the regulatory background, see ACOP L8 and HSG274 explained.

A practical first pass

1. 1

   Walk the system

   Map every tank, cylinder, calorifier, TMV, shower, spray tap and outside tap. Note dead legs and rarely-used outlets.

2. 2

   Measure temperatures

   Hot at sentinel outlets (≥50°C within 1 minute), cold at sentinels (<20°C), calorifier flow/return, cold tank water.

3. 3

   Check tanks and cylinders

   Lids sealed, insect screens fitted, no debris, water below 20°C, cylinder thermostat at 60°C.

4. 4

   Decide what's reasonable

   Remedials for anything out of range. A scheme of control that matches the risk — flushing, monthly temperature checks, periodic tank inspection.

5. 5

   Write it down

   Schematic, risk assessment, scheme of control, log sheets — and a review date.

Frequently Asked Questions

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