Legionella Risk Assessment for Landlords UK 2026: Complete Guide

Legionella risk assessment is a legal obligation for all UK landlords, yet it remains one of the most overlooked compliance requirements. Legionella bacteria can cause Legionnaires' disease, a potentially fatal form of pneumonia, and landlords have a duty under the Health and Safety at Work etc. Act 1974 to assess and control the risk in their rental properties.

The good news is that for most standard residential properties, the risk is low and the assessment is straightforward. You do not necessarily need to hire a specialist. But you do need to understand what legionella is, where it grows, what the risk factors are in your property, and what control measures to implement. Failing to carry out an assessment and implement appropriate controls can result in enforcement action from the Health and Safety Executive (HSE) or local authority.

This guide covers everything UK landlords need to know about legionella risk assessments in 2026, including the legal framework, the assessment process, control measures, documentation requirements, void property procedures, and costs.

What Is Legionella and Why Does It Matter?

Legionella is a genus of bacteria found naturally in freshwater environments. It becomes a health risk when it multiplies in artificial water systems — including domestic water systems in homes — and is then inhaled as fine water droplets (aerosols). The most dangerous species, Legionella pneumophila, causes Legionnaires' disease, a severe pneumonia with a fatality rate of approximately 10% among otherwise healthy individuals and higher among vulnerable groups.

Legionella thrives in water temperatures between 20°C and 45°C. Below 20°C, the bacteria survive but do not multiply significantly. Above 60°C, they are killed within minutes. This temperature range is the critical factor in risk assessment and control.

In the UK, approximately 300-500 cases of Legionnaires' disease are reported annually. While the majority of cases are linked to large commercial and industrial water systems (cooling towers, hospital water systems), domestic systems can and do harbour legionella, particularly in properties that have been empty for extended periods or that have complex plumbing with dead legs and storage tanks.

Legal Framework for Landlords

The legal duty on landlords to assess and control legionella risk comes from several overlapping pieces of legislation:

• Health and Safety at Work etc. Act 1974: Section 3 imposes a duty on employers and self-employed persons to conduct their undertaking in a way that does not expose others to health and safety risks. Letting a property is conducting a business undertaking, and tenants are persons who could be affected.
• Control of Substances Hazardous to Health Regulations 2002 (COSHH): Legionella bacteria are a biological agent that constitutes a substance hazardous to health. COSHH requires assessment and control of exposure.
• HSE Approved Code of Practice L8: "Legionnaires' disease: The control of legionella bacteria in water systems" provides the primary guidance. While ACOP L8 is not legislation, failure to follow it can be used as evidence of non-compliance in enforcement proceedings.
• HSG274 Part 2: "The control of legionella bacteria in hot and cold water systems" provides detailed technical guidance for domestic-type water systems.

The HSE and local authority environmental health departments have the power to inspect properties, require improvements, and prosecute landlords who fail to assess and control legionella risk. While prosecutions of residential landlords specifically for legionella failures are rare, enforcement action is not unheard of, particularly where a case of Legionnaires' disease is traced back to a rental property.

Risk Factors in Residential Properties

Most standard domestic properties with mains-fed water systems (combi boiler, no water storage tank) present a low risk for legionella. However, certain features increase the risk:

For a standard modern property with a combi boiler (which heats water on demand with no storage), mains-fed cold water, and no unusual plumbing features, the legionella risk is generally low. The assessment can often be completed as a simple written record confirming the system type and the absence of high-risk features.

The Risk Assessment Process

A legionella risk assessment follows a standard five-step process aligned with HSE guidance:

1. Identify hazards: Survey the water system to understand how it works. Identify water storage, heating, distribution, and any features that could support legionella growth (tanks, dead legs, complex pipework, infrequent use areas).
2. Assess the risk: Consider who could be exposed and how. Tenants and visitors using showers are the primary risk group. Consider whether any occupants are particularly vulnerable (elderly, immunocompromised).
3. Implement controls: Based on the identified risks, implement appropriate control measures (temperature management, flushing protocols, removing dead legs, maintaining tanks).
4. Record the assessment: Document the findings, the risks identified, and the control measures implemented. Keep this record for the duration of its validity.
5. Review regularly: Review the assessment every two years, or sooner if there are changes to the water system, the property is significantly altered, or there is reason to believe the assessment is no longer valid.

Who Can Carry Out the Assessment?

For simple domestic water systems (combi boiler, mains cold water, no tanks), the HSE accepts that the landlord can carry out the assessment themselves, provided they are competent to do so. Competence in this context means understanding the basics of legionella risk, the water system in the property, and the control measures required.

For more complex systems (cold water storage tanks, hot water cylinders, complex pipework, spa baths), the HSE recommends engaging a person with specific legionella risk assessment training. This does not necessarily mean a specialist company — a competent plumber with legionella awareness training may be sufficient.

• Identify the type of water system (combi boiler, system boiler with cylinder, cold water tank)
• Check hot water is stored at 60°C or above (if applicable)
• Check cold water is below 20°C within 2 minutes of running the tap
• Identify any dead legs or unused outlets
• Check cold water storage tank condition (lid, insulation, overflow, no debris)
• Note any showerheads that may need descaling or replacing
• Check for stagnation risks (unused rooms, void periods)
• Record findings and control measures

Control Measures

Control measures for residential properties are generally straightforward and inexpensive. The key principles are: maintain appropriate temperatures, avoid stagnation, and keep the system clean.

Temperature Management

Hot water should be stored at 60°C or above in the cylinder and distributed so that it reaches 50°C at the tap within one minute of running. Cold water should be maintained below 20°C. If you have a combi boiler with no hot water storage, the temperature control is inherent in the system, as water is heated to over 60°C on demand.

Flushing Protocols

Water stagnation is one of the biggest risk factors. Implement the following flushing protocols:

• Before a new tenancy: Run all taps, showers, and flushing toilets for at least 2 minutes before a new tenant moves in, especially if the property has been void for more than a week.
• Infrequently used outlets: If any taps or showers are rarely used, they should be run weekly for at least 2 minutes. Inform tenants of this requirement in writing.
• After void periods: If the property has been empty for more than 7 days, flush the entire system by running all outlets for at least 5 minutes before occupation.

Showerhead and Tap Maintenance

Showerheads and taps can accumulate scale and biofilm that supports legionella growth. Showerheads should be descaled quarterly (or as needed) and replaced if they cannot be adequately cleaned. Consider providing tenants with descaling instructions, particularly in hard water areas.

Cold Water Tank Maintenance

If the property has a cold water storage tank (typically in the loft), ensure it has a properly fitted lid to prevent debris and contamination, is insulated to keep the water cool, has no dead legs or connections to disused pipework, and is regularly inspected (at least annually). If the tank is in poor condition or no longer needed, consider removing it and converting to mains-fed cold water.

Void Property Procedures

Properties that are empty between tenancies are at elevated legionella risk because water sits stagnant in the pipework at ambient temperature. The longer the void period, the greater the risk.

Best practice for void periods:

• Visit the property weekly and run all water outlets for 2 minutes during prolonged void periods
• If weekly visits are not practical, arrange a thorough system flush before the new tenancy starts
• Check hot water cylinder temperature (should be above 60°C) before the new tenant moves in
• Check cold water temperature at the kitchen tap — should be below 20°C within 2 minutes
• Inspect and clean showerheads, replacing if necessary
• Document the flushing and any checks carried out

If you manage multiple void properties, consider implementing a void property checklist that includes legionella flushing as a standard item. This ensures it is never overlooked during the turnaround process.

Assessment Costs and Documentation

The cost of a legionella risk assessment depends on the complexity of the water system and who carries it out.

Your assessment documentation should include: the date of assessment, the assessor's name and qualifications, a description of the water system (boiler type, whether there are storage tanks, hot water cylinder details), identified risk factors, control measures implemented, any recommendations for further action, and the review date.

Keep the assessment for the duration of its validity (two years for a standard assessment) and retain a copy for at least two years after it is superseded by a new assessment. Provide a copy to your tenants — while this is not a strict legal requirement in the way that gas safety certificates must be provided, it demonstrates good practice and transparency.

Informing Tenants

While there is no specific legal requirement to provide tenants with a copy of the legionella risk assessment, the HSE recommends that landlords provide tenants with information about the water system and any actions they need to take. This is particularly important for control measures that rely on tenant cooperation.

Key information to provide to tenants:

• Do not adjust the hot water thermostat or boiler temperature settings
• Run all taps and showers for 2 minutes after returning from a holiday or period of absence exceeding one week
• Report any changes in water quality (discolouration, unusual smell) immediately
• Do not obstruct or remove showerheads
• Report any plumbing issues promptly (dripping taps, slow drains)
• If the property has a cold water tank, do not access or modify it

Include this information in the tenant welcome pack or as a schedule to the tenancy agreement. A simple one-page information sheet is sufficient for most standard properties.