Legionella Risk in Rental Properties: The Compliance Check Most UK Landlords Forget

Why Legionella isn't optional, even without a certificate

Ask most landlords which checks are legally required on a rental property and you'll get a confident list: Gas Safety, EICR, EPC, smoke and CO alarms. Ask about Legionella risk and the answer is usually a blank look, or "isn't that just for big buildings with cooling towers?"

It isn't. Under the Health and Safety at Work Act 1974 and the Control of Substances Hazardous to Health Regulations (COSHH), anyone who controls premises with a water system — including a landlord letting a single flat — has a legal duty to assess and manage the risk of Legionella bacteria. There's no certificate scheme like a CP12, no fixed renewal date stamped on a wall-mounted plaque, and that's exactly why it gets missed. CertMinder UK exists because "no paperwork required" gets quietly read as "no obligation exists," and with Legionella those are two very different things.

This is informational guidance, not legal advice — for anything property-specific, check current HSE guidance or speak to a qualified assessor.

What the law actually asks for

There is no requirement to hold a formal Legionella certificate for a typical residential letting, and you don't need to hire a specialist every time a tenancy changes hands. What you do need is a documented risk assessment: a record showing you've identified where Legionella could grow in the property's water system and taken reasonable steps to control it.

For most single-let residential properties — a normal domestic hot and cold water system, used regularly, without unusual features like a water storage tank that sits stagnant — this assessment can often be done competently by the landlord or agent themselves, following HSE's ACOP L8 and HSG274 guidance. Where a property has a cold water storage tank, especially one that's rarely used, or where you're letting a larger HMO with a more complex system, a professional assessment is the safer route.

The point isn't to panic landlords into hiring contractors for every property. It's that "we assessed the risk and here's our record" is the actual legal position, and most landlords currently have neither.

Where the risk actually shows up

Legionella bacteria grow in stagnant water sitting between roughly 20°C and 45°C. In a residential letting, the conditions that raise risk are specific and identifiable:

A property that's stood empty between tenancies, especially over a few weeks, lets water sit still in the pipework and any tank. A cold water tank in a loft that never gets flushed is a classic risk point. Shower heads and taps that go unused for stretches — a second bathroom in a property let to a single tenant, for example — accumulate stagnant water in the fittings themselves. And any part of the system running noticeably warm on the "cold" side, often from pipework running too close to hot water pipes or heating, pushes water into the danger temperature band.

None of this requires exotic engineering knowledge to check. It requires someone actually looking, and writing down what they found.

A workable process between tenancies

The simplest control measure, and the one that covers the majority of standard lettings, is running all taps and showers for a few minutes at change of tenancy, particularly after any period the property stood empty. This flushes stagnant water out of the system before a new tenant starts using it daily.

Beyond that, a basic written assessment should record: what water system the property has (mains-fed combi, tank-fed, immersion, etc.), whether there are any storage tanks and their condition, whether hot water is stored and delivered at temperatures that control bacterial growth (typically hot water stored at 60°C or above, and cold water below 20°C), and what you did about anything that fell short — repaired a tank lid, flushed the system, adjusted a thermostat.

Keep that record. It's the document that matters if anything is ever questioned, not a certificate you can point to on a wall.

Where this fits with everything else you're tracking

Legionella sits in an awkward spot for most landlords and agents: it's a genuine legal duty, but it doesn't come with a renewal date, a certificate number, or a contractor phoning to book the annual visit the way Gas Safety does. That's precisely why it's the item most likely to fall through the cracks in a portfolio of any size, and why it's worth treating it with the same discipline as your dated compliance items — assess it, document it, and set a reminder to revisit it, particularly around void periods and tenancy changeovers.

CertMinder UK's reminder and document tracking isn't limited to certificates with fixed renewal cycles — if you want a record of when a property last had a Legionella assessment and a nudge to revisit it after a void period, that's the same kind of tracking you're already using for Gas Safety and EICR. And as always, any contractor you use to help with an assessment is one you choose — CertMinder UK doesn't take a cut from anyone you book, because steering you toward a referral was never the job.

The bottom line

Legionella risk assessment is a genuine legal duty for UK landlords, not an optional extra for big commercial buildings. For most standard residential lettings it's a straightforward, documentable process — flush the system between tenancies, check for stagnant water and tank issues, write down what you found. The failure mode isn't usually a dangerous water system. It's landlords who've simply never been told this applies to them, and who have nothing written down if anyone ever asks.