How to Prevent Legionella in Rental Properties

Yes, and this is the point most commonly misunderstood by residential landlords.

The legal duty to manage Legionella risk is set out in the Health and Safety at Work Act 1974, the Control of Substances Hazardous to Health Regulations 2002 (COSHH), and specifically the HSE's Approved Code of Practice L8 (ACOP L8, the definitive guidance document on Legionella control in the UK.

The HSE's guidance document HSG274 Part 2 makes clear that the duty to assess and manage Legionella risk applies to all landlords of residential premises, not just large commercial operators or multi-storey blocks. If you let a house, flat, or room to a tenant and there is a water system in that property, you have a legal duty of care.

The scale of the measures required is proportionate to the risk. A simple domestic hot-and-cold water system in a small rental property, with no stored water tanks, carries far lower risk than a large HMO with complex pipework and multiple shower points. But the duty to assess that risk and document that assessment exists regardless.

Understanding where Legionella thrives helps you focus your prevention efforts on the highest-risk elements of your property's water system. Legionella bacteria multiply most rapidly in water temperatures between 20°C and 45°C. Below 20°C, bacteria remain dormant but do not multiply. Above 60°C, bacteria are killed within a matter of minutes.

The highest-risk features in a typical residential rental property include:

Hot water storage cylinders (cold water cisterns): Properties with a traditional vented hot water system — rather than a combi boiler — have a cold water storage tank, usually located in the loft. If this tank is not properly insulated, the water temperature inside can drift into the danger zone, particularly during warmer months. Debris and sediment in the tank provide nutrients for bacterial growth.

Showerheads and flexible hoses: Showers represent the highest Legionella transmission risk in residential properties because they produce fine water aerosols that can be directly inhaled. Flexible rubber hoses connected to showerheads are particularly prone to biofilm build-up — a layer of organic material that Legionella bacteria colonise and use as a food source.

Infrequently used outlets: Any tap, shower, or outlet that is left unused for extended periods, a spare bathroom that tenants rarely use, an outside tap, a kitchen mixer tap that is bypassed in favour of a filtered tap, allows water to stagnate in the pipework. Stagnant water in the temperature danger zone is the ideal breeding environment for Legionella.

Complex or poorly designed pipework: Properties with long pipe runs, dead legs (sections of pipework that terminate without a flow-through outlet), or pipework routed near heat sources are at higher risk because water reaches and maintains the danger temperature range more easily.

Water features and spa baths: If your rental property includes a water feature, jacuzzi, or spa bath, these are high-risk items requiring specific management measures and regular maintenance. These are less common in standard residential lettings but should be treated with particular care where present.

The legal obligations for residential landlords under L8 ACOP and HSG274 can be summarised in three core duties:

1. Carry Out a Legionella Risk Assessment

You must assess the risk that your property's water system poses to tenants and any other people who use the property. The risk assessment must:

• Identify potential sources of risk within the water system
• Evaluate the likelihood of Legionella growth given the system's design and condition
• Identify any control measures already in place
• Recommend any additional control measures required
• Be documented in writing

For a straightforward domestic rental property with a combi boiler and no stored water, the risk assessment may be relatively brief. For a property with a cold water storage tank, hot water cylinder, or complex pipework, a more detailed assessment is required.

Who can carry out the risk assessment? The HSE states that a risk assessment can be carried out by the landlord themselves if they are competent to do so — meaning they understand the risks and the control measures required. However, for most landlords, commissioning a professional Legionella risk assessment from a qualified assessor provides far greater protection and documentation quality in the event of a dispute or investigation.

2. Implement and Maintain Control Measures

Once the risk assessment is complete, you must implement the control measures it recommends. These are typically straightforward for residential properties and are detailed in the prevention steps below.

3. Keep Records

You must maintain written records of:

• The risk assessment itself (date, findings, recommendations)
• All control measures implemented
• Any remedial work carried out
• Temperature checks if required by the assessment
• Cleaning and maintenance of water system components

These records are your evidence of compliance. In the event of a tenant contracting Legionnaires' disease and making a claim against you, documented compliance is your primary legal protection.

The following measures address the specific risk factors identified above and form the basis of an effective Legionella prevention programme for a standard residential rental property.

Step 1: Commission a Professional Legionella Risk Assessment

Before implementing any control measures, you need to know what you are dealing with. A professional Legionella risk assessment from a qualified assessor gives you:

• A systematic inspection of your water system — tanks, cylinders, pipework, outlets, and any specialist features
• A written report identifying all risk factors present in your specific property
• Clear, prioritised recommendations for control measures
• Documentation that satisfies your legal duty to assess the risk

For most standard residential properties, a professional risk assessment takes 2–3 hours and produces a written report within a few days. It should be reviewed and updated whenever there is a significant change to the water system or the property, and as a matter of best practice when a new tenancy begins.

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Step 2: Set Hot Water to Store and Distribute at the Correct Temperature

Temperature control is the single most effective Legionella prevention measure available.

Hot water: Your hot water system should store water at a minimum of 60°C and distribute it to all outlets at a minimum of 50°C within one minute of running. At 60°C, Legionella bacteria are killed within two minutes. At 50°C, bacteria are killed within about two hours. Below 50°C at the outlet, the risk rises sharply.

If your property has a hot water storage cylinder, check and confirm that the thermostat is set to at least 60°C. If the current thermostat is inaccurate or inaccessible, have it checked and adjusted by a qualified plumber.

Cold water: Cold water should be stored and distributed at temperatures below 20°C. If your cold water storage tank is located in a loft space that becomes very warm in summer, consider adding or improving insulation around the tank and pipework to keep the temperature below this threshold.

Scalding risk: At temperatures above 50°C, there is a scalding risk — particularly for elderly tenants, young children, and those with reduced sensation or mobility. Thermostatic mixing valves (TMVs) can be fitted at outlets to blend hot water to a safe temperature (typically 41–44°C for a bath, 41°C for a shower) while keeping the stored and distributed water hot enough to control Legionella. Where vulnerable tenants are present, fitting TMVs at high-risk outlets is strongly recommended.

Step 3: Clean and Descale Showerheads Regularly

Showerheads and flexible hoses are among the highest-risk components in a residential property because they produce fine aerosol droplets and are prone to biofilm build-up.

Showerheads should be cleaned and descaled at least every three months. The process involves:

1. Removing the showerhead from the hose
2. Submerging it in a descaling solution — white vinegar works well as a cost-effective alternative to chemical descalers
3. Leaving for a minimum of one hour
4. Rinsing thoroughly with clean water
5. Flushing by running the shower for two minutes before use

Flexible rubber or plastic hoses should be inspected at the same time. If a hose shows signs of deterioration, discolouration, or significant scale build-up, replace it. Stainless steel braided hoses are preferable as they are more resistant to biofilm formation than flexible plastic alternatives.

Make a written record of every cleaning, including the date and what was done. This forms part of your compliance documentation.

Step 4: Flush Infrequently Used Outlets Regularly

Any outlet that goes unused for seven days or more allows water to stagnate in the pipework, creating a higher risk of Legionella growth. Where a rental property has outlets that tenants are unlikely to use regularly, a guest bathroom, an outside tap, a utility room sink, and a written flushing programme should be in place.

Flush all infrequently used outlets for a minimum of two minutes at least once a week. This replaces the stagnant water in the pipework with fresh water from the mains or storage, resetting the temperature and removing any bacterial accumulation. If the property is going to be unoccupied for any period — between tenancies, during a landlord inspection period, or when tenants are on extended holiday, flush all outlets thoroughly before occupation resumes.

Important for void periods: A period of vacancy carries a significantly elevated Legionella risk. Water that has sat stagnant in the system for weeks or months should be fully flushed before any person uses the property. For extended void periods of four weeks or more, a thorough flushing of the entire system, all hot and cold outlets run for several minutes, should be carried out before any occupation.

Step 5: Inspect and Clean Cold Water Storage Tanks

If your property has a cold water storage cistern, typically located in the loft or an airing cupboard, it requires specific maintenance.

The tank should:

• Have a close-fitting, insect-proof lid to prevent contamination from debris, bird droppings, or insects
• Be insulated to maintain water temperature below 20°C
• Be free of internal debris and sediment — tanks should be inspected and cleaned periodically (at least every two years, or more frequently if the risk assessment recommends it)
• Have an appropriate water level — an oversized or overfilled tank means water sits unused for longer, increasing stagnation risk

If the inspection reveals debris, biofilm, or evidence of contamination, the tank should be thoroughly cleaned and disinfected before use. This is specialist work best carried out by a qualified plumber or water hygiene contractor.

Step 6: Inspect and Insulate Pipework

Pipe runs exposed to heat sources, passing through warm cupboards, near boilers, or through uninsulated loft spaces, can raise the temperature of cold-water pipework into the Legionella danger zone.

Check that:

• Cold water pipework is insulated where it passes through warm spaces
• Hot and cold pipework runs are not positioned directly against each other without insulation between them
• There are no dead legs in the system — sections of pipework that branch off but terminate without a live outlet. Dead legs allow water to stagnate and should be removed or capped off at the nearest active junction by a qualified plumber.

Step 7: Provide Tenants With Clear Information

Your tenants are your on-the-ground eyes and ears for water system issues. Providing them with basic information about Legionella risk management serves two purposes: it helps keep the system safer through their day-to-day use and demonstrates your commitment to their safety.

At the start of every tenancy, provide written guidance that covers:

• The importance of running all outlets regularly — particularly those used infrequently
• How to clean showerheads and what signs of scale or discolouration to look out for
• Who to contact if they notice changes to water temperature, pressure, or appearance
• What to do if the property is going to be left unoccupied for a week or more (notify you so flushing can be arranged)

Step 8: Review the Risk Assessment When Circumstances Change

A Legionella risk assessment is not a permanent document. It should be reviewed and updated whenever:

• A new tenancy begins
• The water system is altered — new pipework, new outlets, a boiler replacement, and a tank upgrade
• The property is left unoccupied for an extended period
• There is reason to believe the system may have been contaminated — following a plumbing defect, a water supply interruption, or any unusual change in water appearance, taste, or smell
• The current risk assessment is more than two years old, as a matter of best practice

How often does a Legionella risk assessment need to be renewed? There is no fixed legal renewal period. The HSE requires the assessment to be reviewed whenever there is a relevant change to the system or its use. As a matter of best practice, reviewing the assessment at each change of tenancy and at least every two years is widely accepted as a reasonable approach.

Can I carry out my own Legionella risk assessment? The HSE states that landlords can carry out their own assessment if they are competent to do so. However, competence requires a genuine understanding of Legionella risk factors, water system design, and control measures. For most landlords, a professional assessment provides better documentation quality and more defensible evidence of compliance.

Does a combi boiler property have a lower Legionella risk? Yes. Properties with a combi boiler have no stored hot water; water is heated on demand, and there is no tank. This significantly reduces the Legionella risk compared to properties with hot water cylinders and cold water storage tanks. However, the duty to assess the risk still applies, and showerheads, flexible hoses, and infrequently used outlets remain risk factors even in combination boiler properties.

What if my tenant contracts Legionnaires' disease? If a tenant contracts Legionnaires' disease and can demonstrate that the infection originated in your rental property, you face significant legal liability. Documented compliance with L8 ACOP, including a professional risk assessment and records of all control measures, is your primary legal protection. Without this documentation, defending a claim or prosecution is extremely difficult.

Is Legionella testing the same as a Legionella risk assessment? No. A Legionella risk assessment evaluates the design and condition of your water system to determine the likelihood of bacterial growth. Water testing, taking samples from outlets and sending them for laboratory analysis, checks whether Legionella bacteria are actually present. For most residential properties, a risk assessment is sufficient. Water testing is typically reserved for complex systems, HMOs, or when a case of Legionnaires' disease has been linked to the property.