Legionella Risk Assessments for Landlords: Do You Need One?

Legionella is a type of bacteria that can cause Legionnaires' disease, a potentially fatal form of pneumonia. It grows in water systems where the temperature sits between 20°C and 45°C, and is spread by inhaling fine water droplets — from showers, taps, and cooling towers.

As a landlord, you have a legal duty under health and safety law to assess and control the risk of legionella in your rental properties. This is separate from the electrical and gas safety obligations most landlords are familiar with, but it is equally enforceable.

What Legionella Is and How It Spreads

Legionella pneumophila is a naturally occurring bacterium found in water environments. In low concentrations in the natural environment, it poses minimal risk. In building water systems, it can multiply to dangerous levels if conditions are favourable — warm water, stagnation, and nutrients from scale, sludge, or rust.

The bacteria are spread not by drinking water but by inhaling fine water aerosols (mist). This is why showers are the highest-risk source in domestic properties — they produce fine droplets that can be inhaled deeply into the lungs.

Legionnaires' disease is serious. Around 10% of confirmed cases result in death, and survivors can suffer lasting lung damage. The elderly, smokers, and people with underlying health conditions are at highest risk — but healthy adults have also contracted the disease from contaminated water systems.

Why Landlords Are Responsible

The Health and Safety at Work Act 1974 requires anyone who has control of premises to manage the health and safety of people using those premises. The Control of Substances Hazardous to Health Regulations 2002 (COSHH) specifically cover biological hazards, including legionella.

The HSE's Approved Code of Practice L8 (ACoP L8) — Legionnaires' Disease: The Control of Legionella Bacteria in Water Systems sets out how landlords must comply. While ACoP L8 is primarily aimed at commercial premises and large water systems, the HSE has made clear that landlords of residential properties are also required to comply with the duty to assess legionella risk.

The HSE has published specific guidance for landlords of residential properties (HSG274 Part 2 and the LACORS guidance) which sets out what is required in simple, low-risk domestic settings.

Which Properties Are at Highest Risk

Not all rental properties carry the same legionella risk. The key factors are:

High-risk properties:

• HMOs with multiple showers — shared bathrooms with showers used by multiple occupants, where the shower head may not be cleaned regularly
• Properties with cold water storage tanks — older properties often have a cold water tank in the loft, which can allow water to stagnate and warm in summer months
• Properties with a hot water cylinder — where the stored hot water temperature is not maintained at 60°C or above
• Properties left empty for extended periods — stagnant water at moderate temperatures is ideal for legionella growth
• Properties with complex or old pipework — dead legs (sections of pipe that are rarely used) allow water to stagnate

Lower-risk properties:

• Properties with a combi boiler and direct mains cold water supply (no storage tank, no stored hot water)
• Properties with modern, simple plumbing with no dead legs or infrequently used outlets
• Properties with regular occupancy where water is used daily and does not stagnate

What ACoP L8 Requires

ACoP L8 requires the duty holder (the landlord) to:

1. Identify and assess the risk of legionella in the water system
2. Prepare a written scheme for managing identified risks
3. Implement and manage the scheme — including regular checks and maintenance
4. Keep records of actions taken
5. Appoint a responsible person (which can be the landlord themselves for simple systems)

For simple residential properties (combi boiler, mains cold water, regular occupancy), the risk is typically low and the control measures are basic: flush infrequently used outlets regularly, check that the hot water temperature is adequate, and instruct tenants on shower head hygiene.

For higher-risk properties, a professional water hygiene assessment and ongoing monitoring programme may be required.

What a Legionella Risk Assessment Involves

A professional legionella risk assessment for a residential rental property typically includes:

System survey:

• Identification of all water outlets (taps, showers, toilets, appliances)
• Identification of the cold water supply type (mains or storage tank)
• Identification of the hot water system (combi, stored cylinder, immersion)
• Identification of any dead legs or infrequently used outlets

Temperature checks:

• Cold water temperature at key points (should be below 20°C at the point of use)
• Hot water temperature at key points (should reach 50°C within one minute of running, indicating the cylinder or flow is above 60°C)

Risk evaluation:

• Assessment of whether the system configuration creates conditions for legionella growth
• Identification of higher-risk features (storage tanks, complex pipework, infrequently used outlets)

Written report and action plan:

• Overall risk rating for the property
• Specific control measures recommended
• Any immediate actions required (e.g., cleaning a shower head with scale, flushing a stagnant outlet, increasing hot water temperature)

How Often to Reassess

The risk assessment should be reviewed:

• On a change of tenancy — new tenants, change of occupants in an HMO
• After any significant plumbing works — changes to the water system require a re-assessment
• After a period of vacancy — properties left empty for more than a week should be flushed through before occupancy
• Periodically — even without changes, a review every two years is best practice for properties with storage tanks or complex systems

For simple, low-risk properties (combi boiler, single occupancy), the review may simply confirm that conditions remain low risk and no additional controls are required.

What Happens If Someone Contracts Legionnaires' Disease at Your Property

If a tenant or visitor contracts Legionnaires' disease and it is traced to your property, the consequences are severe:

Criminal prosecution by the HSE: The HSE has prosecuted landlords for failing to maintain adequate water hygiene controls where a case of Legionnaires' disease has been linked to a property. Prosecution is under the Health and Safety at Work Act and carries an unlimited fine. Imprisonment is possible for serious cases.

Civil liability: A tenant who contracts Legionnaires' disease from inadequate water hygiene in your property has a civil claim for damages against you as the landlord. Damages for a serious illness can be substantial.

Reputational and regulatory impact: A prosecution or civil claim will typically come to the attention of the local housing authority, potentially triggering broader compliance inspections of your portfolio.

The most effective protection is a documented risk assessment and evidence that you have implemented the recommended control measures.

How to Control Legionella Risk in Practice

For most domestic rental properties, the practical steps are straightforward:

For properties with combi boilers and mains supply:

• Instruct tenants to flush any outlet (tap or shower) that has not been used for more than a week before use
• Ensure shower heads are cleaned and descaled periodically (this can be written into the tenancy agreement)
• Keep a record of the risk assessment and the control measures in place

For properties with storage tanks:

• Ensure the cold water tank has a lid and is insulated from heat sources
• Check that the hot water cylinder thermostat is set to 60°C or above
• Flush the system at the start of each tenancy after a vacancy
• Consider annual temperature monitoring

For HMOs with multiple shower rooms:

• More rigorous assessment required — professional assessment recommended
• Regular cleaning and descaling of shower heads
• Temperature monitoring programme
• Written records of all checks

Cost of a Legionella Risk Assessment in London

A professional legionella risk assessment for a standard residential rental property in London costs approximately £300. The assessment includes a written report, risk rating, and recommended control measures.

For HMOs and properties with complex water systems, pricing depends on the size and complexity of the installation. Contact our team for a quote via the legionella risk assessment page.