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Legionella Risk Assessment: A Practical Guide for Property Owners and Businesses
London Chlorination & Water Treatments
A water system may appear clean and operate normally while still containing conditions that encourage bacterial growth.
For landlords, businesses, property managers and other dutyholders, understanding these risks is an important part of protecting building occupants and maintaining water hygiene.
A professional Legionella risk assessment helps identify potential hazards, examine existing control measures and establish what improvements may be necessary.
This practical guide explains the main areas an assessment should cover and how to maintain effective water hygiene.
What Is a Legionella Risk Assessment?
A Legionella risk assessment is a structured review of a water system to identify circumstances that could allow Legionella bacteria to multiply and expose people to contaminated aerosols.
Legionella bacteria can develop in water systems when conditions are favourable, particularly where there is poor temperature control, stagnation or an accumulation of nutrients such as sediment and biofilm.
An assessment considers the building's water system, how it is used and who may be exposed.
Its purpose is to identify practical control measures appropriate to the actual risks.
Who Is Responsible for Managing Legionella Risks?
Responsibilities depend on who controls the premises and its water systems.
Employers, landlords, managing agents and facilities managers may have duties under health and safety legislation.
For more complex buildings, several organisations may share operational responsibilities.
Clearly identifying who manages inspections, maintenance, monitoring and corrective actions is essential.
An effective risk management programme should not leave important responsibilities undefined.
1. Understand the Water System
Before potential hazards can be managed, the building's water system must be properly understood.
An assessment may examine:
Cold water storage tanks
Hot water cylinders and calorifiers
Distribution pipework
Taps, showers and other outlets
Thermostatic mixing valves
Infrequently used sections
Water circulation arrangements
Areas where water may stagnate
For larger buildings, an accurate schematic diagram can help identify concealed or complicated sections of the system.
Where the assessment reveals deteriorating or unsuitable components, hot and cold water system replacements may be considered as part of the remedial works.
2. Check Water Temperatures
Temperature management is one of the main methods used to control Legionella risks.
UK Health and Safety Executive guidance generally recommends keeping cold water below 20°C where possible, storing hot water at 60°C or above, and achieving appropriate distribution temperatures.
Temperature monitoring should be based on the system's configuration and the risk assessment.
Checks at representative and sentinel outlets can help identify areas that are not maintaining the intended conditions.
Where temperature control problems are identified, the cause should be investigated rather than relying solely on additional disinfection.
3. Identify Stagnant Water and Unused Outlets
Water that remains unused for extended periods can create conditions favourable to bacterial growth.
Common examples include:
Spare bathrooms
Infrequently occupied offices
Seasonal accommodation
Unused showers
Redundant pipework
Buildings that have been temporarily closed
A suitable management programme may include regular flushing and the removal of unnecessary pipework.
Where stagnant or altered pipework requires treatment, pipework disinfection may form part of the recommended corrective action.
4. Inspect Water Storage Tanks
Storage tanks require appropriate inspection and maintenance.
Over time, sediment, scale and other deposits can accumulate within the system.
A poorly maintained tank may undermine wider water hygiene controls.
When the assessment identifies contamination or unsuitable tank conditions, water tank cleaning can help address the problem.
The cleaning and inspection frequency should reflect the system's condition, usage and risk assessment findings.
5. Maintain Showers, Taps and Associated Equipment
Showers and taps are important because they can produce aerosols through which Legionella bacteria may be inhaled.
Showerheads and hoses can accumulate scale, making regular cleaning and descaling important.
Thermostatic mixing valves should also be incorporated into appropriate inspection and maintenance arrangements.
Maintaining individual outlets helps support the wider water hygiene programme.
6. Take Action on Assessment Findings
A risk assessment is only effective when its recommendations are implemented.
Depending on the findings, remedial measures may include:
Improved temperature control
Regular flushing of low-use outlets
Removal of redundant pipework
System repairs or replacements
Water testing and sampling, where indicated
Not every system requires all these measures. The correct approach depends on the risks identified and the applicable guidance.
7. Keep Records and Review the Assessment
Water hygiene management is an ongoing responsibility.
Records should reflect the controls being implemented, including relevant temperature checks, inspections, maintenance and corrective actions.
A Legionella risk assessment does not have a universal annual expiry date. It should be reviewed regularly and whenever there is reason to believe it may no longer be valid.
Changes in building use, occupancy, water systems or control effectiveness may trigger a review.
Arrange a Legionella Risk Assessment in London
London Chlorination & Water Treatments supports landlords, commercial property owners, facilities managers, councils and homeowners with water hygiene services across London.
Our Legionnaires assessment service helps property owners understand potential risks and identify suitable control measures.
Where further work is needed, we also provide tank cleaning, pipework disinfection, chlorination and water testing services.
Contact London Chlorination & Water Treatments to discuss your property and request a free, no-obligation quote.
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