Legionella Risk Assessment in London: What It Covers and Who Needs One

What Legionella Is and Why Water Systems Pose a Risk

Legionella pneumophila is a bacterium found naturally in water environments. In building water systems, the bacterium can multiply to dangerous concentrations in conditions that favour its growth: temperatures between twenty and forty-five degrees Celsius, stagnation allowing biofilm development, and the presence of nutrients such as scale, sediment, and corrosion products. When water containing a high concentration of legionella bacteria is inhaled as a fine aerosol, such as the droplets produced by a shower, spa, or cooling tower, there is a risk of developing Legionnaires disease, a severe and potentially fatal form of pneumonia.

London properties face a specific legionella management challenge because they are served by hot water systems in buildings of widely varying age, design, and condition. Many older London properties have complex water systems with long pipe runs, dead ends, and infrequently used outlets that create the stagnation conditions in which legionella can proliferate. The duty to manage legionella risk in London buildings is a legal obligation under the Health and Safety at Work Act 1974 and the Control of Substances Hazardous to Health (COSHH) Regulations, supported by the Approved Code of Practice L8 published by the Health and Safety Executive.

Who Has a Legal Duty to Assess Legionella Risk in London

The L8 Approved Code of Practice imposes a duty to manage legionella risk on all persons who have control of premises in which water systems could give rise to legionella exposure. For London residential landlords, this means every tenanted property where there is a hot water system. The Health and Safety Executive has confirmed that the duty applies to residential landlords renting domestic properties, not only to commercial premises operators. A London landlord who has never carried out a legionella risk assessment for their tenanted properties has not complied with the legal duty.

For commercial premises in London, including offices, hotels, care homes, leisure facilities, and any premises with cooling towers or evaporative condensers, the legionella management duty is more extensive and the consequences of non-compliance are more serious. The HSE and local authority environmental health officers conduct inspection programmes targeting commercial premises, and failure to have a current legionella risk assessment in place is a prosecutable offence under the Health and Safety at Work Act.

What a Proper Legionella Risk Assessment Covers

A legionella risk assessment for a London property must identify and evaluate all potential sources of legionella risk within the water system. For a typical domestic rental property in London, this involves a physical inspection of all cold water storage tanks or cisterns, the hot water cylinder and its thermostat settings, all heating and hot water distribution pipework that is accessible, all outlets including showers, baths, taps, and any garden irrigation connections, and any areas where water may stagnate due to infrequently used outlets or dead leg pipework.

The assessor should record water temperatures at representative outlets and at the cylinder thermostat, checking that the hot water storage temperature is maintained at a minimum of sixty degrees Celsius and that hot water is delivered at the outlet at no less than fifty degrees Celsius within one minute of running. Cold water should be delivered at below twenty degrees Celsius at the outlet within two minutes of running. These temperature parameters are the most critical control measure for legionella risk in domestic water systems.

The assessment should identify any conditions that represent elevated risk, such as a hot water cylinder with an insufficient thermostat setpoint, pipework serving infrequently used outlets such as a guest bathroom shower used only occasionally, a cold water cistern with no lid or insulation, or pipework passing through areas where the temperature may be elevated by proximity to heating equipment. Each risk identified should be accompanied by a recommended control measure and a timescale for implementation.

What the Assessment Should Produce

A compliant legionella risk assessment produces a written report that identifies the duty holder, describes the scope of the assessment, records the water system as found including temperatures, identifies risks and their severity, recommends control measures and timescales, and establishes a review date or trigger for reassessment. The assessment should be retained by the duty holder as evidence of compliance and updated whenever there is a change to the water system or at a minimum every two years for straightforward domestic systems.

For landlords, the written assessment should be provided to the tenant or made available on request, and a record of any control measures implemented should be maintained alongside the assessment document. Prestige Engineers carry out legionella risk assessments for London landlords and commercial properties across all boroughs, producing fully compliant written assessments and implementing any recommended remedial measures as part of the same visit where practical.