Legionella risk assessment

A Legionella risk assessment is the formal process by which a landlord identifies whether the water systems in a rental property could support the growth of Legionella bacteria, evaluates the level of risk to occupants, and determines the control measures needed to keep that risk low. Under the Control of Substances Hazardous to Health Regulations 2002 (COSHH) and Section 3(2) of the Health and Safety at Work Act 1974, landlords are legally required to assess and control the risk of Legionella exposure in any property they let. The Health and Safety Executive (HSE) confirms that for most residential properties this is a proportionate, low-burden obligation, not a requirement for specialist contractors or formal certification.

What is Legionella and why does it matter?

Legionella is a bacterium found naturally in water environments. When it colonises a domestic hot or cold water system and reaches the right conditions, water temperatures between 20°C and 45°C, stagnation, and a supply of scale, rust, or biofilm, it can multiply to concentrations capable of causing Legionnaires' disease. Legionnaires' disease is a potentially fatal form of pneumonia contracted by inhaling water droplets containing the bacteria, most commonly from showers, taps, or stored water systems. It cannot be caught from drinking water. While cases in straightforward residential properties are rare, the obligation to assess the risk applies to every landlord regardless of property type or scale.

What does a Legionella risk assessment involve?

A risk assessment for a residential rental property should cover the following:

identifying all hot and cold water systems present, including storage tanks, cylinders, pipework, showers, and taps; assessing whether conditions exist that favour bacterial growth, particularly water temperatures in the 20–45°C range or evidence of stagnation; identifying who might be affected, with particular attention to tenants who are elderly, immunocompromised, or otherwise vulnerable; evaluating existing control measures and their adequacy; and recording the findings and any actions taken.

From working with self-managing landlords across the UK, we know that many approach Legionella as a source of unnecessary anxiety. For properties with a combi boiler, mains-fed cold water supply, and regular occupancy, the assessment will almost always confirm low risk and require nothing beyond simple maintenance habits. The HSE is explicit that the assessment should be "practical and proportionate", a phrase that means the depth of scrutiny should match the complexity of the water system, not a standard template applied to every property regardless of design.

Who can carry out the assessment?

The HSE confirms that most residential landlords can carry out a Legionella risk assessment themselves without specialist training or accreditation. The requirement is that the assessor is competent, meaning they understand what Legionella is, know the factors that increase colonisation risk in domestic settings, and can identify appropriate control measures. No formal certificate of competence is required for a straightforward residential property.

If a property has complex water systems, open-top cold water storage tanks, multiple hot water cylinders, long pipe runs, or cooling infrastructure, the assessment may benefit from professional input. Landlords who are uncertain about their competence to assess a specific system should commission a qualified contractor. Properties with higher-risk occupants, such as supported housing or houses in multiple occupation with shared water systems, warrant more detailed assessment regardless of system complexity.

Is a Legionella test certificate required?

No. Health and safety law does not require landlords to obtain or produce a Legionella test certificate, and no such certificate formally exists. Some letting agents request one as a condition of taking on a property; this practice has no legal basis and the HSE has addressed it directly. What the law requires is that a risk assessment is carried out and that identified risks are controlled, not that any specific document is produced. Water sampling and laboratory testing for Legionella bacteria is similarly not a statutory requirement for residential properties, and is only warranted in specific circumstances where a higher-risk system is present or where the assessment identifies it as necessary.

Landlords do not need to record their assessment findings unless they employ five or more people, this is the statutory threshold for written records under health and safety legislation. That said, keeping a simple written record of what was assessed and when is sensible practice, particularly as evidence of compliance if a tenant later raises a concern.

Control measures

The most reliable control measure for domestic water systems is temperature management: hot water should be stored at 60°C or above, distributed at 50°C or above at the point of use, and cold water should remain below 20°C throughout. Where thermostatic mixer valves are fitted to limit scald risk at outlets, they should be installed as close to the outlet as possible.

Beyond temperature, the HSE recommends the following practical steps: flush the system thoroughly before each new tenancy begins; flush all outlets at least weekly during void periods to prevent stagnation; keep cold water tanks (where fitted) covered to exclude debris; remove any dead legs or redundant pipework; and advise tenants to clean and disinfect showerheads regularly and to report any problems with hot water delivery. Properties with instantaneous water heaters, such as combi boilers or electric showers, carry lower inherent risk because there is no stored water in which bacteria can multiply.

Landlords using August consistently tell us that Legionella is one of the compliance obligations most easily embedded into routine property management, a brief check during the gas safety visit or before each new tenancy is usually all that is needed for low-risk residential properties.

How often should the assessment be reviewed?

The law does not specify a fixed review interval. The HSE requires that the assessment be reviewed whenever there is reason to believe it may no longer be valid, for example, after significant changes to the water system, after a period of extended vacancy, at the start of a new tenancy, or if a water-related health concern is reported. Best practice in the sector is to review the assessment at least every two years for properties where the water system is simple and low-risk, and annually where the system is more complex or where tenants with vulnerability are present.

For a full picture of what landlord compliance looks like in practice, the August EICR guide sets out how safety inspections fit into the broader obligation framework.

Statutory context

The legal duty rests primarily on Section 3(2) of the Health and Safety at Work Act 1974 and the Control of Substances Hazardous to Health Regulations 2002. Detailed guidance is set out in the HSE's Approved Code of Practice Legionnaires' disease: The control of legionella bacteria in water systems (L8), which has the same legal status as a statutory code, departure from it must be demonstrably justified. The HSE's dedicated landlord guidance page confirms the proportionate application of these duties to residential lettings and should be the first reference point for any landlord carrying out their own assessment.

Properties with gas appliances carry an overlapping compliance obligation, the annual gas safety certificate is equally non-negotiable and is worth coordinating with the Legionella assessment where access allows.

Frequently asked questions

Do all landlords have to carry out a Legionella risk assessment? 

Yes. The obligation applies to every landlord who lets a property under a lease or licence shorter than seven years, regardless of whether they manage one property or a portfolio. The scope of the assessment should be proportionate to the complexity of the water system, a basic check suffices for most straightforward residential properties.

Can a landlord carry out the assessment themselves? 

In most cases, yes. The HSE states that most residential landlords are capable of assessing the risk in their own properties without specialist training. The person carrying out the assessment must be competent to do so, meaning they understand Legionella risk factors in domestic settings and can identify appropriate control measures. A professional assessor is warranted for complex or higher-risk systems.

What temperature kills Legionella bacteria? 

Legionella does not survive above 60°C. The HSE recommends that hot water be stored at 60°C or above and distributed at 50°C or above at the outlet. Cold water should be kept below 20°C, as bacterial growth accelerates in the 20–45°C range.

Does a Legionella risk assessment expire? 

There is no statutory expiry period. The assessment should be reviewed whenever circumstances change, after significant works to the water system, at the start of a new tenancy, following a void period, or if a water-related health issue arises. A periodic review every one to two years is generally considered best practice.

August's compliance tracker logs your Legionella assessment alongside gas safety and EICR records, so no obligation slips through the gaps.

This definition reflects UK law as of 1 May 2026. The Renters' Rights Act 2025, in force from 1 May 2026, does not alter Legionella obligations, which continue to rest on the Health and Safety at Work Act 1974, COSHH 2002, and the L8 Approved Code of Practice.