Legionella Risk Assessment When Selling

Legionella bacteria and Legionnaires' disease rarely come up in the context of domestic property sales. For most sellers of owner-occupied homes, they do not need to. But if you are selling a property that has been let, or if the subject arises during conveyancing enquiries, it helps to understand what the legal position is, what a legionella risk assessment actually involves, and what practical steps are needed to comply.

This guide covers the legal framework around legionella in residential properties, when an assessment is required, what it examines, how much it costs, and what sellers — particularly landlords — need to have in order when selling an investment property.

What is Legionella and why does it matter?

Legionella pneumophila is a bacterium found naturally in water environments. When present in sufficient concentrations and inhaled as fine water droplets (aerosols), it can cause Legionnaires' disease — a severe and potentially fatal form of pneumonia. It can also cause Pontiac fever, a milder flu-like illness.

Legionella thrives in water systems where specific conditions are met: water temperatures between 20°C and 45°C, the presence of nutrients such as scale, rust, sludge, or organic matter, and water that is allowed to stagnate or sit unused for extended periods. In domestic properties, the components most associated with legionella risk are:

• Cold water storage tanks in the loft, particularly older tanks that may be uncovered, inadequately insulated, or corroded
• Hot water cylinders set to temperatures below 60°C
• Showers, which create the fine aerosols through which legionella bacteria can be inhaled
• Infrequently used outlets such as en suite bathrooms, spare room showers, or guest toilets
• Dead legs in pipework — sections of pipe that are no longer in active use and allow water to pool

Properties on a direct cold water mains supply with a combi boiler — where there is no stored cold water and no hot water cylinder — have the lowest inherent risk, because water flows directly from the mains rather than being stored.

The legal position for sellers

Owner-occupier sellers

If you live in the property you are selling and have been its only occupant, there is no legal requirement to carry out a legionella risk assessment before or during the sale. The legal duty to assess and manage legionella risk arises under the Health and Safety at Work etc. Act 1974, the Management of Health and Safety at Work Regulations 1999, and the Control of Substances Hazardous to Health Regulations 2002 (COSHH). These obligations apply to employers, those in control of non-domestic premises, and landlords — not to private homeowners selling their own residence.

In practice, legionella rarely appears in the TA6 Property Information Form or in conveyancing enquiries for standard residential sales. It is not a field on the form and is unlikely to be raised by the buyer's solicitor unless there is a specific reason — for example, if the property has a hot tub, cooling system, or complex water feature that might attract attention.

Landlords selling a rental property

The position is different if you are selling a property that has been let out. Under HSE guidance — specifically the Approved Code of Practice L8 (Legionnaires' disease: The control of legionella bacteria in water systems) and Technical Guidance HSG274 — landlords have a legal duty of care to assess the risk from legionella bacteria in their rental properties. This duty has applied since 2014 when revised HSE guidance clarified that it extended to all residential landlords, not just those managing large or complex installations.

When you sell a rental property, the buyer's solicitor will carry out due diligence on how the property has been managed, and for an investment buyer, legionella compliance is part of that picture. A current legionella risk assessment should be available to share with the buyer's side along with other property management documentation. For an overview of the full set of documentation typically expected when selling a rental or investment property, see our dedicated guide on that topic.

What does a legionella risk assessment cover?

A residential legionella risk assessment is an examination of the entire water system in a property to identify conditions that could allow legionella bacteria to proliferate and to determine what control measures, if any, are needed to manage that risk. A competent assessor will examine:

Cold water supply and storage

The assessor will check whether the property receives cold water directly from the mains or whether it is stored in a tank, usually in the loft. If there is a cold water storage tank, the assessor will inspect it for:

• Coverage (the tank must be covered to prevent contamination)
• Temperature (cold water should be stored and supplied below 20°C — if the tank is in a warm loft without adequate insulation, it may warm above this)
• The condition of the tank interior, looking for signs of corrosion, scale, sludge, or other contamination
• The design of the system, including whether there are any sections where water could stagnate

Hot water system

Where the property has a hot water cylinder (vented or unvented), the assessor will check the stored temperature. Hot water should be stored at a minimum of 60°C to prevent legionella survival and distributed at no less than 50°C at all outlets. The assessor will also check whether there are any sections of hot pipework where temperatures might drop into the danger zone of 20°C to 45°C.

Distribution pipework and outlets

The assessor will examine the pipework layout, looking for:

• Dead legs — sections of pipe that terminate without an active outlet, where water can sit and warm to temperatures favourable for legionella growth
• Infrequently used outlets such as en suite showers, spare bathroom taps, or outdoor taps, where water stagnation is likely
• The condition of showerheads and hoses, which can harbour scale and biofilm

Any water features or specialist systems

If the property has a hot tub, spa bath, decorative water feature, swimming pool, or cooling tower, these are higher-risk items that require specific attention. Hot tubs and spa baths are among the most significant sources of Legionnaires' disease in domestic settings because they operate at temperatures that can support bacterial growth, they create aerosols, and they may not be regularly maintained or chlorinated properly.

Risk levels in domestic properties

For most straightforward domestic properties, the legionella risk is low. The HSE acknowledges this in its guidance and does not expect landlords to commission expensive specialist surveys for standard houses or flats. The following table summarises the typical risk level by property type:

Practical control measures

For most domestic properties, managing legionella risk involves a handful of straightforward precautions rather than complex engineering controls. The HSE's guidance for residential properties recommends the following:

1. Set the hot water cylinder to 60°C. This is the single most important control measure for properties with a stored hot water system. At 60°C, legionella bacteria are killed within two minutes. The temperature at outlets should be at least 50°C within one minute of running the tap.
2. Keep cold water cold. Cold water should be stored and supplied below 20°C. Insulate cold water pipes that run through warm areas, and ensure the cold water storage tank (if present) is adequately insulated and located away from heat sources.
3. Flush infrequently used outlets regularly. Any tap, shower, or outlet that is used less than once a week should be flushed for at least two minutes weekly to prevent water stagnation. This is particularly important for en suite bathrooms, spare rooms, or guest facilities.
4. Clean and descale showerheads quarterly.Showerheads and hoses can accumulate scale and biofilm that provide nutrients for legionella. Remove and clean them in a dilute bleach solution at least every three months.
5. Keep cold water tanks covered and clean.If the property has a cold water storage tank in the loft, it must be covered with a close-fitting lid to prevent contamination from dust, insects, or animals. Check it annually and clean it if there are signs of sludge, scale, or contamination.
6. Remove dead legs. If plumbing works have left redundant pipework, arrange for a plumber to remove it to eliminate stagnation risk.
7. Flush the system after vacancy. If the property has been empty — whether between tenancies, during renovation, or during a void period before sale — flush the entire water system thoroughly before occupation. Run all taps, showers, and outlets for at least two minutes.

How legionella fits into the sale process

On the TA6 form

Legionella is not a named question on the current edition of the TA6 Property Information Form. Sellers will not be directly asked whether a legionella risk assessment has been carried out. However, the TA6 does include questions about compliance with regulations and any notices received from authorities, and the general duty to disclose material information under the property certificate pack and the principle of seller disclosure means that you should not knowingly withhold relevant information about the property's water system if it is material.

Conveyancing enquiries for rental properties

When selling a rental property, the buyer's solicitor will raise enquiries covering the property's compliance with landlord obligations. These typically include questions about gas safety, electrical safety, energy performance, smoke and carbon monoxide alarms, and — particularly for solicitors acting for experienced investors — legionella risk. If you are selling a tenanted property, having a current legionella risk assessment ready to provide alongside the gas safety record and EICR will demonstrate that the property has been professionally managed and reduce the volume of follow-up questions. For more on the hidden costs and compliance requirements involved in selling a house, see our costs guide.

How it relates to boiler and water system documentation

Legionella risk assessment sits naturally alongside other water system and property maintenance documentation. If you have a current boiler service record, a gas safety certificate, and an EICR, a legionella risk assessment completes the picture for a well-managed property. For the relationship between boiler maintenance and property sales more generally, see our guide on boiler service records when selling.

How to get a legionella risk assessment

Who can carry it out?

The HSE requires that a legionella risk assessment is carried out by a competent person. For straightforward domestic properties, a competent person can include the landlord themselves, provided they have sufficient knowledge and understanding of the relevant risks and control measures. The HSE has published free guidance specifically for landlords and small premises that outlines what a basic assessment should cover.

For more complex systems, or where the landlord lacks the knowledge to conduct a reliable assessment, a specialist water hygiene consultant or a company accredited by the Legionella Control Association (LCA) should be used. Many plumbing and building services companies also offer residential legionella assessments.

What the assessment should produce

Whether carried out by the landlord or a specialist, the assessment should result in a written record that includes:

• A description of the water system, including a basic schematic if the system is complex
• Identification of all potential risk sources and the conditions found at the time of inspection
• An assessment of the risk level for each identified source
• Recommended control measures and the actions taken or planned to address any risks identified
• The name and role of the person who carried out the assessment and the date it was completed

This written record is the document that a buyer's solicitor or a local authority environmental health officer would ask to see. Keeping it updated is good practice regardless of any sale.

Cost

A professional legionella risk assessment for a standard residential property typically costs between £60 and £150. The price varies by property size, system complexity, and provider. Properties with cold water storage tanks, multiple bathrooms, or specialist water features will be at the higher end. Some building services companies and estate management firms offer assessment packages that include legionella alongside gas safety and EICR inspections.

Properties where legionella risk is higher

Certain property types and situations warrant more careful attention to legionella risk when selling:

• HMOs (Houses in Multiple Occupation). Properties let to multiple households have more complex water systems, higher occupancy, and a greater potential for misuse of water controls. HMOs are subject to mandatory licensing requirements, and legionella compliance forms part of the HMO licensing regime. If you are selling an HMO, a comprehensive legionella risk assessment by a specialist is expected.
• Properties with hot tubs or spas. These represent the highest domestic legionella risk. If a property being sold has a hot tub or spa pool, the seller should be able to demonstrate that it has been maintained properly, the water has been treated, and a risk assessment specific to the installation has been carried out.
• Older properties with traditional water systems.Pre-1980s properties are more likely to have cold water storage tanks, older cylinders, and pipework configurations that create stagnation risk. If the property has not been updated to a modern, mains-fed system, a thorough legionella assessment is advisable.
• Properties that have been empty for a long period.An empty property is one where water stagnation risk is highest. If the property has been unoccupied during probate, a lengthy renovation, or a void period between tenancies, the water system should be flushed thoroughly before any marketing viewings and before occupation by a new buyer. Consider having a formal assessment done if the property has been empty for more than a few weeks.

Seller's checklist for legionella

Use the following checklist to confirm your position on legionella before listing or during the sale process:

1. Confirm whether you are selling as an owner-occupier or a landlord — the legal obligations differ significantly
2. If selling a rental property, check that a current legionella risk assessment is in place and documented
3. Verify that the hot water cylinder (if present) is set to at least 60°C
4. Check that cold water storage tanks are covered, clean, and below 20°C
5. Flush all infrequently used outlets before viewings and before handing over the property
6. Clean showerheads and check for any visible scale or biofilm
7. If the property has been empty, flush the entire water system before marketing
8. If the property has a hot tub, spa, or cooling system, ensure maintenance records and a specific risk assessment are available
9. Gather the assessment document and control measure records to provide to the buyer's solicitor alongside other compliance certificates

Sources

• Health and Safety Executive (HSE) — L8 Approved Code of Practice and Guidance: Legionnaires' disease: The control of legionella bacteria in water systems (4th edition) — hse.gov.uk
• HSE — HSG274 Technical guidance on legionella: Part 2 — hse.gov.uk
• HSE — Legionella and legionnaires' disease: A brief guide for dutyholders — hse.gov.uk/pubns/indg458
• Health and Safety at Work etc. Act 1974 — legislation.gov.uk
• Control of Substances Hazardous to Health Regulations 2002 (COSHH) — legislation.gov.uk
• Legionella Control Association (LCA) — legionellacontrol.com
• Law Society — TA6 Property Information Form, 4th edition

Frequently asked questions