What Is a Legionella Risk Assessment? London Landlord Guide
Legionella risk assessments are a legal obligation for London landlords. What Legionella is, why London properties are at risk, what the assessment involves, and what actions it typically recommends.
What Is Legionella?
Legionella pneumophila is a bacterium that causes Legionnaires' disease — a serious form of pneumonia. It grows in water systems where conditions are favourable: temperatures between 20–45°C, stagnant water, scale, and organic material (biofilm). Legionnaires' disease is contracted by inhaling contaminated water droplets — typically from showers, hot tubs, and cooling towers.
Legal Requirement for London Landlords
The Health and Safety at Work etc. Act 1974 and the Control of Substances Hazardous to Health Regulations 2002 (COSHH) place a duty of care on London landlords to assess and control the risk of Legionella in their rental properties. The HSE's Approved Code of Practice L8 and Technical Guidance HSG274 provide detailed guidance.
In practice: all London landlords of residential rental properties must carry out a Legionella risk assessment and implement any control measures identified.
What a Legionella Risk Assessment Covers
A residential Legionella risk assessment in London examines:
- The type of hot and cold water system (combi boiler, vented/unvented cylinder, cold storage tank)
- Water temperatures — hot water should be stored at 60°C+ and delivered at 50°C+ at outlets within 1 minute
- Cold water supply and storage — cold water should be below 20°C at outlets
- Dead legs — sections of pipework that rarely see flow (unused outlets, disconnected circuits)
- Infrequently used outlets (showers in guest rooms, taps rarely used)
- Scale and corrosion in the system
- Thermostatic mixing valves (TMVs) — set to 41°C to prevent scalding, but must have anti-Legionella flushing capability
Legionella Risk in London Rental Properties
London rental properties are often at elevated Legionella risk because: multiple occupants with irregular usage patterns create stagnant water in parts of the system; HMOs may have long pipe runs with dead legs; older London properties may have cold water header tanks in lofts that warm above 20°C in summer; and high tenant turnover means properties may sit empty for periods allowing water to stagnate.
Frequently asked questions
How often does a London landlord need a Legionella risk assessment?
The HSE does not specify a fixed frequency for residential Legionella risk assessments — the requirement is to review the assessment when there are changes to the water system, occupancy, or when there is reason to believe it may no longer be valid. In practice, most London property professionals recommend reassessment every 2 years, or sooner if: the property sits empty for more than a month; a major plumbing change is made; the tenancy changes; or Legionella risk factors change (e.g. a new shower installed).
Who can carry out a Legionella risk assessment in London?
A Legionella risk assessment can be carried out by any competent person — there is no statutory requirement for a specific qualification, unlike gas safety (Gas Safe) or electrical (NIC EIC/NAPIT). However, for the assessment to be credible and defensible, it should be carried out by someone with knowledge of L8 and residential water systems. Our engineers carry out Legionella risk assessments as part of combined compliance visits for London landlords.
What are the typical recommendations in a London landlord Legionella risk assessment?
Typical recommendations from a residential Legionella risk assessment in London include: setting the boiler or hot water cylinder to 60°C+; installing thermostatic mixing valves (TMVs) at showers to prevent scalding while allowing hot storage; flushing infrequently used outlets weekly (or removing dead legs); replacing cold water header tanks with sealed, insulated alternatives; and advising tenants to run showers for 2 minutes after periods of non-use. Most London properties only require low-cost control measures.