Legionella risk assessments: what landlords actually have to do
22 September 2026 · AgentCheck Editorial · 7 min read
Part of our UK Landlord Legal Guide
Landlords have a duty to assess and control the risk of exposure to legionella bacteria in the properties they let. What they do not have is a legal obligation to buy a "legionella certificate", and the HSE says so plainly. For a typical single let with mains-fed cold water and a combi boiler, a short written assessment you carry out yourself is enough. Water sampling is not normally required in domestic systems. The properties that do warrant a specialist are the ones with stored water, communal systems or long periods of non-use.
This is the compliance item landlords are most reliably sold something they do not need. A letter arrives, usually from a company you have never dealt with, warning that your legionella certificate has expired and offering to renew it for an annual fee. Some agents quietly add it to the management bill as a mandatory annual cost. It is worth knowing exactly what the law asks for, because the gap between the duty and the product being sold is wide.
Where the duty comes from
There is no legionella-specific statute for landlords. The duty comes from general health and safety law: the Health and Safety at Work etc. Act 1974, which requires those conducting an undertaking to protect people other than their employees from risks arising out of it, and the Control of Substances Hazardous to Health Regulations 2002, which treat biological agents including legionella as a substance hazardous to health. The Approved Code of Practice known as L8 sits on top of these and sets out how to comply.
Because this is health and safety law rather than housing law, it applies across Great Britain. Most of the tenancy rules landlords deal with are England-only, so this is one of the few areas where a landlord with property in Scotland or Wales is looking at broadly the same duty.
The duty is to assess the risk and put reasonable control measures in place. It is not a duty to produce a document to a prescribed format, to renew anything annually, or to engage a contractor. The HSE has been explicit that health and safety law does not require landlords to obtain or produce a legionella test certificate.
Why most rented homes are low risk
Legionella needs three things to become a problem: water sitting at a temperature between roughly 20 and 45 degrees, something for the bacteria to feed on such as scale, rust or biofilm, and a way of turning contaminated water into a breathable aerosol, most commonly a shower.
A modern single let removes most of that. Mains-fed cold water arrives cold and is used daily. A combi boiler heats water on demand, so there is no stored volume sitting lukewarm. Occupied properties have constant turnover through taps, showers and washing machines. The HSE position is that risks in most residential settings are low precisely because of this regular use, and that a detailed assessment is not needed.
What raises the risk
The features worth paying attention to are the ones that create standing water at the wrong temperature:
- A cold water storage tank in the loft, particularly an uninsulated one, an uncovered one, or one you have never actually looked inside.
- A stored hot water cylinder, especially if the thermostat has been turned down to save money, or an immersion heater used only intermittently.
- Dead legs: sections of pipework that go nowhere, often left behind when a bathroom was moved or a shower removed and the pipe capped rather than cut back.
- Outlets that are rarely used. A guest en-suite, an outside tap, a second bathroom in a large house let to a small household.
- Long void periods. An empty property with nobody running the taps is exactly the condition that lets bacteria establish.
- Spa baths, whirlpool baths and electric showers with heavily scaled heads.
- Communal systems: a block with a shared calorifier, or a large HMO with a stored hot water system serving multiple bathrooms. These are genuinely a different proposition and do justify professional assessment.
Doing the assessment yourself
For a standard single let, this is an hour of work and one side of paper. There is no prescribed form. A useful record covers:
- A plain description of the water system. Mains-fed or tank-fed, combi or cylinder, how many outlets, whether there are showers, whether there is any pipework you know to be redundant.
- The risk factors you found, and the ones you checked and ruled out. Writing "no cold water storage tank, loft inspected" is more useful than silence.
- The control measures. For most properties: hot water stored hot, cold water kept cold, outlets used regularly, showerheads descaled and cleaned periodically, and the system flushed after any void.
- Who does what, and when you will look at it again.
- The date and your name.
On temperature, the principle the HSE repeats is to keep hot water hot, cold water cold, and keep it moving. Where water is stored, hot storage should be hot enough to control bacterial growth and cold water should stay below 20 degrees. Be sensible about scalding at the same time, particularly if the tenant is elderly or there are young children, which is what thermostatic mixing valves are for.
There is no legal review interval. The sensible trigger is change: a new tenancy, a boiler replacement, a bathroom refit, a long void, or anything the tenant reports. Tying the review to your mid-tenancy inspection keeps it from being forgotten.
Voids and the flush that actually matters
If a property has stood empty for weeks, the single most useful thing you can do before the next tenant moves in is run every outlet. Run the cold taps until the water runs properly cold, run the hot until it runs properly hot, and flush the toilets. For showers, remove the head if you can and run the hose into the bath, or bag the head to contain spray, because that is the one outlet that produces the aerosol you are worried about. Descale and clean the head while it is off.
This matters more for student properties than almost any other type, because a long summer void followed by six people arriving on the same day is precisely the pattern the guidance warns about.
Tell the tenant, in writing
Part of controlling the risk is information the tenant can act on. Include a short note in the welcome pack asking them not to adjust the boiler or cylinder thermostat, to run taps and showers that have not been used for a week or more before using them normally, to clean and descale showerheads from time to time, and to tell you if the hot water is not getting properly hot or the cold is running warm. That last one is a genuine early warning, and most tenants will not think to mention it otherwise.
So what about the certificate?
If a company or an agent tells you a legionella certificate is a legal requirement for a standard domestic let, that is wrong. Ask them to point to the requirement. What you may reasonably choose to buy is a professional risk assessment, and for a property with a stored water system, a communal supply, a large HMO or a system you genuinely do not understand, that is money well spent. For a two-bed flat with a combi boiler, it is a form-filling exercise you can do yourself.
Water sampling is a separate thing again and is not normally warranted in domestic systems. It tells you about one outlet at one moment and does nothing to control the risk. Temperature and turnover do the work.
If you use a managing agent, ask specifically whether legionella assessment is included in the management fee or charged separately, and what they actually do for it. It is one of the line items worth interrogating when you are handing a property over to an agent, because a recurring annual charge for something that should be a periodic review adds up quickly across a portfolio.
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