Legionella is the regime most surrounded by confusion and mis-selling. Landlords are told they need an annual "legionella certificate" from a specialist; estates teams over-spend on testing they don't need or skip the assessment they do. Here's what the law actually asks for.

Here's the TL;DR

It's a duty to assess and control, not to certify — under the Health and Safety at Work etc. Act 1974 and COSHH 2002, whoever controls the premises must assess and manage the risk of legionella in the water system. The HSE's Approved Code of Practice is L8, with technical detail in HSG274.
No fixed interval — review the assessment regularly and whenever something changes. Roughly every two years is common good practice, sooner if the system or its use changes.
There is no legal "legionella certificate" — the HSE has been explicit that landlords are not required to produce one. The requirement is a risk assessment plus sensible controls.
Breaches are criminal — failures under the 1974 Act carry unlimited fines and imprisonment.

What legionella is and why it's regulated

Legionella bacteria grow in water systems and cause Legionnaires' disease, a potentially fatal pneumonia, when contaminated water is inhaled as a fine spray — from showers, taps, cooling towers, spa pools. The risk rises in water held between roughly 20–45°C, in stagnant water, and where there's scale or biofilm to feed on.

Because it's a workplace and premises hazard, it's governed by the Health and Safety at Work etc. Act 1974 and the Control of Substances Hazardous to Health Regulations 2002 (COSHH), interpreted through the HSE's Approved Code of Practice L8 and guidance HSG274.

Who's responsible

The duty falls on the duty holder — the employer, the person in control of the premises, or the landlord. For most rented homes the duty holder is the landlord or managing agent. You must:

assess the risk of exposure to legionella;
if there's a foreseeable risk, introduce and manage controls;
keep records of the assessment and the controls;
and review it.

A competent person must do the assessment, but for a typical domestic let that's often a straightforward exercise — not necessarily an expensive specialist visit. Larger or more complex systems (care homes, schools, anything with tanks, calorifiers or cooling towers) need proportionately more.

How often to review

There's no statutory frequency. The duty is to review the assessment regularly and whenever there's reason to believe it's no longer valid — for example after changes to the water system, the building's use, or following any case of the disease. As a working rule, many duty holders review around every two years, and re-check sooner on any material change.

Day-to-day controls are usually simple and ongoing rather than annual: keep hot water hot and cold water cold, flush little-used outlets, avoid stagnation, keep the system clean.

The certificate myth

This matters because it's where money gets wasted. The HSE has stated plainly that landlords are not required to obtain a "legionella test certificate" and that routine testing is usually unnecessary for simple domestic systems. If a contractor is selling you an annual certificate for a two-bed flat, you're likely paying for something the law doesn't require. What you do need is a documented assessment and evidence you're managing the risk.

What happens if you don't

The HSE and local authorities enforce under the 1974 Act. Breaches carry unlimited fines and imprisonment, and duty holders have been prosecuted following outbreaks. The record of your assessment and controls is your defence.

Where it fits

Legionella sits alongside fire, electrical and gas in the statutory set — see the complete UK property compliance guide.

Unlike the others, legionella has no neat expiry date printed on a certificate — which is exactly why it gets forgotten. Proprietas lets you set the review cadence per site, tracks it as a first-class obligation, and reminds you before it lapses, so the one regime without a hard deadline doesn't become the one you overlook. See how it works.

This is a plain-English overview, not legal advice — your duties depend on your premises and water systems.

Legionella risk assessments: who needs one and how often