Legionella Risk in London Rental Properties: What Landlords Are Required to Do

Legionella and the Legal Duty on London Landlords

Legionnaires disease — a severe form of pneumonia caused by the Legionella bacteria — is a genuine public health risk in domestic water systems. London landlords have a legal duty under health and safety legislation to assess and control this risk in their rental properties. The duty is not widely understood, and compliance levels in the London private rented sector are inconsistent. This guide explains precisely what the law requires, what a risk assessment involves, and what practical control measures are necessary for different types of property.

The Legal Basis for the Landlord Duty

The primary legal duty on landlords arises from the Health and Safety at Work Act 1974, Section 3, which requires employers and self-employed persons to conduct their undertakings in a way that does not expose non-employees to health and safety risks. A landlord operating a rental business is a self-employed person conducting an undertaking, and their tenants are non-employees who may be exposed to Legionella risk from the water systems in the property. This duty is supplemented by the Control of Substances Hazardous to Health (COSHH) Regulations 2002, under which Legionella bacteria is a biological hazard requiring risk assessment.

L8 ACoP and HSG274

The Health and Safety Executive has published the Approved Code of Practice L8 (Legionnaires Disease: The Control of Legionella Bacteria in Water Systems), which sets out the framework for assessing and controlling Legionella risk. The companion guidance HSG274, Parts 1 to 3, provides detailed technical guidance for specific system types. L8 has the special status described earlier in this guide: it is not law, but failure to follow it is taken as evidence of non-compliance with the underlying legislation in enforcement proceedings. For practical purposes, following L8 is the minimum standard London landlords should meet.

What Legionella Is and Why Domestic Water Systems Present a Risk

Legionella bacteria are naturally present in low concentrations in freshwater environments. They become a health risk when they proliferate to high concentrations in artificial water systems and are then dispersed in water droplets small enough to be inhaled into the lungs. The conditions that allow Legionella to proliferate are well established: water temperatures between approximately 20 and 45 degrees Celsius are the optimal growth range; stagnation allows the bacteria to multiply without dispersal; sediment, scale, and biofilm in pipework provide nutrients and protection. Domestic hot and cold water systems in residential properties can create all of these conditions, particularly where the system includes hot water storage or infrequently used outlets.

High-Risk vs Lower-Risk Systems

Not all domestic water systems present the same level of Legionella risk. The highest-risk residential systems are those with hot water storage cylinders where the temperature across the entire stored volume cannot be reliably maintained at 60 degrees Celsius or above, complex pipework configurations with dead legs or infrequently used branches, and systems serving multiple units from shared plant (HMOs and small blocks). A simple system consisting of a combi boiler (which has no stored hot water), mains cold supply directly to taps, and no cold water storage tank is considered lower risk. The L8 guidance acknowledges that for simple combi boiler systems, the risk assessment may conclude that the risk is low and that no specific further control measures are needed beyond maintaining the system and flushing infrequently used outlets.

What a Risk Assessment Covers

A Legionella risk assessment for a London residential property involves a survey of the hot and cold water system including all storage vessels, all pipe runs, all outlets (taps, showers, bidets), and any other components through which water passes. The assessor checks water temperatures at the cylinder (which should reach 60 degrees), at sentinel outlets (the hot tap furthest from the boiler and the cold tap furthest from the incoming mains), and at other representative outlets. A schematic of the pipework is produced, identifying any dead legs, infrequently used outlets, or other risk factors. The assessment concludes with a written report and, where risks have been identified, a control scheme specifying the measures to be implemented.

Control Measures for London Rental Properties

The primary control measures for Legionella risk in domestic water systems are: maintaining hot water at 60 degrees Celsius at the storage cylinder (this kills Legionella within two minutes); maintaining cold water below 20 degrees Celsius throughout the system; flushing infrequently used outlets (outlets not used for seven days or more) for at least two minutes before use to remove stagnant water; and removing dead legs from pipework where identified. For properties with storage cylinders, a calibrated thermostatic mixing valve (TMV) should be set to deliver blended hot water at a maximum of 50 degrees Celsius at outlets accessible to tenants and children, balancing the scald risk against the Legionella control temperature requirement.

Record Keeping

The L8 ACoP requires that Legionella risk assessment and control activities are documented. For a simple residential let, the minimum documentation is a written risk assessment, a record of any temperature checks carried out, and a record of any remedial actions taken. These records should be retained for the duration of the tenancy and for a minimum period thereafter. In the event of an enforcement investigation or a claim arising from a Legionella incident, these records are the primary evidence of compliance.

Who Should Carry Out the Assessment

The L8 ACoP requires that a Legionella risk assessment is carried out by a "competent person" with sufficient knowledge, training, and experience to understand the risks and the control measures. For a simple residential let with a combi boiler and no storage, many landlords can carry out and document their own assessment using the HSE guidance. For more complex systems — HMOs with shared hot water cylinders, properties with old lead pipework, or any system where the risk assessment identifies factors requiring engineering judgment — a specialist water treatment or building services consultant should be engaged. UKAS accreditation is not required for residential assessments, but professional indemnity insurance is advisable for consultants offering this service.

Costs in London

For a simple single-tenancy residential let in London with a combi boiler system, a professional Legionella risk assessment typically costs between £80 and £150. For a house in multiple occupation (HMO) or a property with a hot water cylinder and more complex pipework, the cost is typically £150 to £300 or more. These costs are modest relative to the legal exposure of non-compliance and the reputational and financial consequences of a Legionella incident in a managed property. Many London letting agents now require landlords to have a current Legionella risk assessment as a condition of management.

Common Failings in London Properties

The most common Legionella risk control failings found in London rental properties during professional assessments are: hot water cylinders set at too low a temperature (below 60 degrees) to save energy; cold water storage tanks in roof voids without insulation, allowing summer temperatures to rise above 20 degrees; showers with flexible hoses and heads that are rarely cleaned, providing ideal conditions for biofilm growth; dead legs from previous plumbing layouts left in pipework; and no documented assessment or control records. Each of these failings is straightforward to address once identified, which underlines the value of a professional assessment as a starting point for compliance.