Legionella and Hot Water Temperature for London Landlords
London landlords have a legal duty to manage the risk of Legionella in domestic hot water systems. This guide explains the temperature requirements, what a risk assessment involves, and how to protect tenants and comply with the law.
What Is Legionella and Why It Matters for Landlords
Legionella pneumophila is a bacterium that occurs naturally in water. In low concentrations in the natural environment, it is harmless. It becomes a health risk when it colonises a man-made water system — a hot water cylinder, a cooling tower, a spa pool, or a domestic hot water distribution system — and proliferates to dangerous concentrations. A person who inhales aerosol droplets from contaminated water can contract Legionnaires disease, a potentially fatal form of pneumonia. In England and Wales, approximately 300 to 400 cases of Legionnaires disease are reported annually, with domestic hot water systems implicated in a significant proportion of residential cases.
The Health and Safety Executive and the Health and Safety at Work Act 1974 place a duty on employers to manage Legionella risk in workplaces. For residential landlords, the Approved Code of Practice L8 (Legionella bacteria: The control of legionella, hygiene, "safe" hot and cold water systems) sets out the expected standard of management. The HSE has confirmed that this duty applies to residential landlords in rented properties as well as employers in workplaces.
Temperature as the Primary Control Measure
Legionella grows optimally at temperatures between 20 and 45 degrees Celsius. Below 20 degrees Celsius, growth is inhibited. Above 60 degrees Celsius, the bacteria die within minutes. The primary control measure in domestic hot water systems is therefore temperature management — keeping stored hot water at a minimum of 60 degrees Celsius to prevent bacterial proliferation, and ensuring hot water reaches the outlets at a temperature above 50 degrees Celsius within one minute of running the tap.
For immersion heater-heated cylinders, the thermostat must be set to a minimum of 60 degrees Celsius. For combination boiler systems that heat water on demand rather than storing it, the Legionella risk is lower because there is no stored volume of water at risk temperature — but the hot water outlets should still be checked to confirm delivery temperature. For stored hot water cylinders (both vented and unvented), the thermostat setting is the critical control.
Legionella Risk Assessment for Rented Properties
A Legionella risk assessment for a domestic rented property does not require the complexity of an industrial system assessment. The HSE guidance for simple domestic systems is proportionate — the landlord or a competent person should inspect the hot and cold water system, identify any risk factors (dead legs, infrequently used outlets, cold water storage tanks, stored hot water below 60 degrees Celsius), and implement corrective measures where risks are identified. The assessment should be documented and reviewed annually or whenever the system changes significantly.
Prestige Engineers carries out Legionella risk assessments for London landlords as part of an annual plumbing service visit or as a standalone inspection. We check thermostat settings, test hot water outlet temperatures with a calibrated thermometer, inspect cold water storage tanks where present, identify dead-leg pipework, and provide a written assessment report. The assessment can be combined with an annual boiler service visit for portfolio landlords with multiple properties. Contact us for Legionella risk assessment and hot water temperature compliance across all London boroughs.