Legionella Risk Assessment HA9

Legionella pneumophila is the bacterium responsible for Legionnaires' disease, a potentially fatal form of pneumonia. It thrives in water systems where temperatures sit between 20°C and 45°C, where water is stored or recirculated, and where nutrients such as rust, scale, or biofilm are present. Infection occurs when contaminated water is aerosolised — through showers, taps, or spray outlets — and the droplets are inhaled.

London rental properties carry a disproportionate risk compared to owner-occupied homes. The city's housing stock is old: Victorian and Edwardian terraces with long copper pipe runs, basement tanks, and gravity-fed systems are common across HA9 and the wider city. These configurations create the conditions Legionella needs — water sitting at lukewarm temperatures in dead-legs, cisterns, and poorly insulated pipes.

HMOs introduce additional complexity. Multiple bathrooms, shared water systems, and fluctuating occupancy mean water can sit stagnant in little-used outlets for days. Thermostatic mixing valves (TMVs), installed to prevent scalding, can harbour Legionella if not correctly set and serviced. Long pipe runs from the boiler to the furthest bathroom in a converted Victorian house are a textbook risk factor.

Commercial properties in HA9 face further hazards: cooling towers, evaporative condensers, spa pools, and recirculating hot water systems all feature on the HSE's list of high-risk water systems. Even a small office building with a water storage tank and a single shower facility requires a formal assessment.

The legal basis for Legionella control in rental property sits under the Control of Substances Hazardous to Health Regulations 2002 (COSHH). Regulation 6 requires employers and the self-employed to carry out a suitable and sufficient assessment of the risk of exposure to substances hazardous to health — and Legionella bacteria is explicitly listed as such a substance by the HSE.

For residential landlords, the HSE confirmed in 2014 that Legionella risk assessment is a legal requirement for all domestic lets, regardless of property size. The obligation flows from the Landlord and Tenant Act 1985 duty to keep installations in repair and proper working order, read alongside COSHH. Failure to carry out an assessment and implement suitable controls can result in enforcement action, civil liability if a tenant contracts Legionnaires' disease, and invalidation of your landlord insurance.

The HSE Approved Code of Practice L8 ("Legionnaires' disease: The control of Legionella bacteria in water systems") sets the practical standard for compliance. An L8 ACOP compliant written report identifies all water systems, categorises risk levels, specifies control measures, and sets a programme for ongoing monitoring. It is the document your insurer, local authority HMO licensing officer, and HSE inspector will ask to see.

A risk assessment is not the same as Legionella monitoring. The assessment identifies hazards and determines control measures. Monitoring — checking hot water temperatures, flushing infrequently used outlets, inspecting storage tanks — is the ongoing programme that flows from the assessment. Both are required. The HSE recommends reviewing the risk assessment annually or whenever the water system changes significantly.