Legionella Risk Assessments: What Every Landlord and Letting Agent Needs to Know

Legionella Risk Assessments: What Every Landlord and Letting Agent Needs to Know

Legionella bacteria thrive in warm, stagnant water. When contaminated water is aerosolised -- through a shower head, a tap, or a cooling system -- occupants can inhale droplets containing the pathogen, potentially developing Legionnaires' disease: a severe and sometimes fatal form of pneumonia. In the UK, landlords and letting agents have a clear legal duty to assess and control the risk of legionella exposure in every property they let. Despite this, legionella risk assessments remain one of the most commonly overlooked compliance obligations in the private rented sector.

This guide explains what the law requires, what a competent assessment actually involves, and how to build a practical water safety management regime that protects both your tenants and your legal position.

The Legal Framework: Why Legionella Assessments Are Non-Negotiable

UK landlords' obligations around legionella stem from several overlapping pieces of legislation. Understanding these is essential, because ignorance of the law is not a defence if a tenant falls ill.

The Health and Safety at Work etc. Act 1974

Section 3 of this Act places a duty on employers and self-employed persons -- including landlords -- to conduct their undertakings in a way that does not expose non-employees (i.e. tenants) to risks to their health and safety. Providing rented accommodation is considered an "undertaking" for the purposes of the Act, which means the duty applies to all landlords, not just those with employees.

The Control of Substances Hazardous to Health Regulations 2002 (COSHH)

COSHH requires the assessment of risks from hazardous substances, including biological agents such as legionella bacteria. Landlords must identify and assess the risk of legionella exposure from the water systems in their properties and take proportionate steps to prevent or control that risk.

The Management of Health and Safety at Work Regulations 1999

These regulations reinforce the duty to carry out a suitable and sufficient assessment of the risks to health and safety of any persons not in their employment arising out of or in connection with the conduct of their undertaking. For landlords, this directly covers legionella risk in rented properties.

HSE Approved Code of Practice L8

The Health and Safety Executive's Approved Code of Practice L8, titled "Legionnaires' Disease: The Control of Legionella Bacteria in Water Systems," is the cornerstone guidance document. While not legislation in itself, L8 has a special legal status: compliance with its recommendations is treated as evidence that you have met your legal duties, and failure to follow it can be used against you in enforcement proceedings. L8 applies to all premises where water is stored or used and where there is a reasonably foreseeable risk of legionella exposure. That includes virtually every residential rental property.

HSG274 Part 2

HSG274 is the technical companion to L8, published in three parts. Part 2 specifically addresses hot and cold water systems -- the type found in residential properties. It provides detailed practical guidance on temperature control, system design, maintenance frequencies, and monitoring procedures.

Who Needs a Legionella Risk Assessment?

The short answer: every landlord letting a residential property in England, Wales, Scotland, or Northern Ireland. The HSE has confirmed that landlords of residential accommodation have a duty to assess the risks from legionella to their tenants. This obligation applies regardless of the size of the property, the type of tenancy, or the number of tenants. A single-bedroom flat with a combi boiler carries the same legal duty as a large house of multiple occupation (HMO) with a hot water storage tank and multiple bathrooms.

Letting agents who manage properties on behalf of landlords should also pay close attention. If you have taken on management responsibilities for a property, you may share the duty holder obligations under health and safety law. Contractual arrangements between landlord and agent should make clear who is responsible for commissioning and acting on legionella assessments.

What Does a Legionella Risk Assessment Involve?

A competent legionella risk assessment is a systematic evaluation of the property's water system to identify conditions that could allow legionella bacteria to grow and be transmitted to occupants. It is not a water test in the usual sense -- the assessor is not sampling water for bacteria (although laboratory testing may be recommended in some circumstances). Instead, the assessment focuses on the design, condition, and operation of the water system and the risks it presents.

Hot Water System Inspection

The temperature at which hot water is stored and delivered is one of the most critical control measures against legionella. The bacteria multiply rapidly between 20 degrees Celsius and 45 degrees Celsius, with optimal growth at around 37 degrees Celsius. Above 60 degrees Celsius, legionella is killed.

A competent assessor will check:

- Hot water storage temperature -- The water in hot water cylinders, calorifiers, or thermal stores should be stored at a minimum of 60 degrees Celsius. The assessor will verify that the boiler or immersion heater is set correctly and that the stored water actually reaches this temperature.
- Hot water distribution temperatures -- Water should reach taps at 50 degrees Celsius or above within one minute of running. The assessor will measure temperatures at representative outlets throughout the property to check for heat loss in distribution pipework.
- Thermostat and control settings -- Incorrectly set thermostats, energy-saving modes that reduce storage temperatures below 60 degrees Celsius, or faulty thermostatic mixing valves (TMVs) can all create conditions favourable to legionella growth.

Properties with combi boilers that heat water on demand and have no stored hot water generally present a lower risk than those with hot water storage tanks, but they are not exempt from assessment.

Cold Water System Inspection

Cold water should remain cold. If cold water temperatures rise above 20 degrees Celsius, the risk of bacterial colonisation increases significantly. The assessor will check:

- Cold water storage tanks -- Properties with header tanks or cold water storage cisterns in loft spaces are a particular concern. The assessor will inspect the tank for correct lid fitting, insulation, debris, and signs of contamination. Loft-mounted tanks exposed to summer heat can easily exceed safe temperature thresholds.
- Cold water temperatures at taps -- Temperatures should be below 20 degrees Celsius within two minutes of running the tap. The assessor will take readings at multiple outlets.
- Mains supply arrangement -- Whether the property is fed directly from the mains or via a storage tank affects the overall risk profile.

Dead Legs and Redundant Pipework

One of the most common risk factors in residential properties is redundant or little-used pipework. When water sits stagnant in pipes that no longer serve an active outlet -- perhaps because a washing machine connection was capped off or a bathroom was reconfigured -- it creates an ideal environment for bacterial growth. The stagnant water in these "dead legs" can then contaminate the wider system when it eventually mixes with flowing water.

A thorough assessment will trace the pipework layout to identify any dead legs, capped-off branches, or infrequently used outlets and recommend their removal or regular flushing.

Showers, Baths, and Aerosol-Generating Outlets

Showers are the highest-risk domestic outlet for legionella transmission because they produce fine aerosol droplets that can be inhaled deep into the lungs. The assessor will inspect:

- Shower heads and hoses -- Condition, cleanliness, and evidence of scale or biofilm build-up.
- Shower type -- Electric showers with small internal reservoirs, mixer showers fed from stored water, and thermostatic showers each present different risk profiles.
- Spa baths and jacuzzi-type fittings -- These are high-risk items due to their aeration systems and the potential for water to remain in internal pipework between uses.

External Taps and Hose Connections

Outdoor taps and garden hoses are easily overlooked but present a genuine risk. Water sitting in a hose exposed to sunlight can rapidly warm to temperatures ideal for legionella growth. When the hose is next used, that warm stagnant water can be aerosolised. The assessor will note any external water outlets and recommend appropriate controls.

The Written Report

Following the physical inspection, the assessor produces a written report documenting:

- A description of the water system and its components.
- The risk level identified (typically categorised as low, medium, or high).
- Specific findings, including any deficiencies or non-compliances.
- Prioritised recommendations for remedial actions.
- A suggested monitoring and maintenance regime going forward.

This report becomes your primary evidence of compliance. It should be retained for the duration of the tenancy and beyond, and updated whenever significant changes are made to the water system.

How Often Should Assessments Be Carried Out?

L8 does not prescribe a fixed reassessment interval, but the HSE recommends that the assessment should be reviewed regularly and certainly whenever there is reason to suspect it is no longer valid. In practice, industry consensus for residential properties is:

- Full reassessment every two years as a minimum, or more frequently for higher-risk properties (e.g. HMOs, properties with vulnerable occupants, or those with complex water systems).
- Review after any significant change to the water system, such as replacement of the boiler or hot water cylinder, alteration of pipework, or a change of use.
- Review between tenancies -- a void period followed by a new tenancy is a natural trigger to verify that water temperatures are correct and that the system has been adequately flushed.

Ongoing Management: What Landlords Must Do Between Assessments

A risk assessment is not a one-off exercise. It establishes the baseline, but ongoing management is what actually controls the risk. Depending on the findings of the assessment, landlords should implement some or all of the following measures:

Temperature Monitoring

- Ensure hot water is stored at 60 degrees Celsius or above.
- Check that hot water reaches outlets at 50 degrees Celsius or above within one minute.
- Verify cold water is delivered below 20 degrees Celsius within two minutes.

For properties managed by agents, a simple temperature check at each routine property inspection (typically quarterly or six-monthly) is good practice and easy to document.

Flushing Infrequently Used Outlets

Any tap, shower, or other water outlet that is not used for a week or more should be flushed by running both hot and cold water for at least two minutes. This is particularly important during void periods between tenancies. Letting agents should build flushing into their void property management checklist.

Descaling and Cleaning Shower Heads

Shower heads and hoses should be cleaned and descaled at least quarterly. Scale deposits and biofilm provide a physical habitat for legionella bacteria and reduce the effectiveness of temperature-based control. Where practical, consider replacing shower heads annually -- they are inexpensive components relative to the risk they can harbour.

Maintaining Cold Water Tanks

If the property has a cold water storage tank, ensure the lid is secure and properly fitted, the tank is insulated, there is no debris or contamination, and the overflow and warning pipes are properly screened to prevent ingress of insects or vermin.

Record Keeping

Document all monitoring, maintenance, flushing, and remedial actions. In the event of a legionella incident or an HSE investigation, your records are the primary evidence that you took reasonable and proportionate steps to control the risk. A simple logbook -- physical or digital -- is sufficient, provided it is kept consistently.

Common Misconceptions

"My property only has a combi boiler, so I don't need an assessment."

Incorrect. While combi boiler systems are generally lower risk because they do not store hot water, the legal duty to carry out a risk assessment still applies. The assessment may conclude that the risk is low and that minimal ongoing controls are needed, but the assessment itself must still be done and documented.

"I only rent to students / young professionals, so the risk is low."

The risk of legionella exposure is determined by the water system, not the tenant demographic. While immunocompromised individuals, smokers, and those over 45 are at higher statistical risk of developing Legionnaires' disease, any person can be infected. The legal duty is to assess the risk to all occupants.

"A gas safety check covers legionella."

It does not. A Gas Safe registered engineer inspecting a boiler is assessing combustion safety, flue integrity, and gas tightness. They are not conducting a legionella risk assessment and are unlikely to check cold water tanks, dead legs, shower heads, or distribution temperatures in the manner required by L8.

"I had an assessment done when I bought the property five years ago."

An outdated assessment is almost as problematic as having no assessment at all. Water systems change, components age, tenants alter usage patterns, and the assessment must reflect the current condition and use of the property.

Enforcement and Penalties

The HSE and local authorities have the power to inspect premises, issue improvement notices, and prosecute landlords who fail to comply with their duties under health and safety legislation. Penalties for non-compliance can include:

- Improvement notices requiring specific actions within a defined timescale.
- Prohibition notices preventing the use of a water system until it is made safe.
- Criminal prosecution -- in serious cases, particularly where a tenant has contracted Legionnaires' disease, landlords can face prosecution under the Health and Safety at Work Act. Unlimited fines and, in the most serious cases, custodial sentences are possible.

Beyond criminal liability, a landlord who fails to carry out a legionella risk assessment may face civil claims from tenants, difficulties with insurance coverage (many landlord insurance policies require compliance with health and safety legislation as a policy condition), and problems satisfying the due diligence requirements of letting agents.

Choosing a Competent Assessor

There is no statutory licensing scheme for legionella risk assessors in the UK, which means landlords need to exercise due diligence when selecting a provider. Look for:

- Relevant qualifications -- City & Guilds qualifications in legionella risk assessment, or equivalent.
- Membership of a professional body -- Such as the Legionella Control Association (LCA), which maintains a register of member organisations.
- Experience with residential properties -- Commercial legionella assessors may not be familiar with the specific risks and system configurations found in domestic settings.
- Insurance -- Professional indemnity and public liability insurance appropriate to the work.
- A clear, comprehensive report -- The output should be a detailed, property-specific document with actionable recommendations, not a generic template with tick boxes.

Practical Steps for Letting Agents

For letting agents managing portfolios of properties, a systematic approach to legionella compliance is essential:

1. Audit your portfolio -- Identify which properties have current, valid legionella risk assessments and which are overdue or have never been assessed.
2. Commission assessments for all properties lacking current documentation. Batch ordering across a portfolio can reduce per-property costs.
3. Build legionella into your management processes -- Include temperature checks in routine inspections, flushing in void property procedures, and assessment review dates in your compliance calendar.
4. Communicate with landlords -- Ensure property owners understand their obligations and that management agreements clearly allocate responsibility for legionella compliance.
5. Retain records centrally -- Keep assessment reports, monitoring logs, and remedial action records in a structured, easily retrievable system. Digital property management platforms can automate reminders and centralise documentation.

Conclusion

Legionella risk assessments are a legal requirement for all UK landlords, not an optional extra. The good news is that for most standard residential properties, the risk is manageable and the controls are straightforward: maintain correct water temperatures, eliminate stagnation, keep systems clean, and document everything. The assessment itself provides the roadmap, and consistent follow-through on its recommendations is what keeps tenants safe and keeps landlords on the right side of the law.

The cost of a competent legionella risk assessment is modest -- typically between 50 and 150 pounds for a standard residential property. The cost of non-compliance, measured in enforcement action, civil liability, insurance complications, and above all the potential harm to a tenant's health, is incomparably greater. If your properties are not assessed, now is the time to act.