Legionella Control & Water Hygiene
What is it?
Legionella bacteria colonise domestic and industrial water systems at temperatures between 20°C and 45°C. Inhalation of contaminated water aerosol droplets causes Legionnaires’ disease, a potentially fatal pneumonia.
Who is responsible?
The Statutory Duty Holder (employer or person in control of premises) and their formally designated Nominated Responsible Person for Water Hygiene.
What needs to happen?
- 01Maintain hot water storage at 60°C minimum and distribution at 50°C minimum (55°C in healthcare) at sentinel taps within 1 minute of running.
- 02Maintain cold water distribution below 20°C at sentinel taps within 2 minutes of running.
- 03Inspect cold water storage tanks annually for sediment, ingress, microbial slime, and pest mesh integrity.
- 04Descale, clean, and disinfect showerheads and hoses quarterly or as indicated by inspection.
- 05Flush little-used water outlets weekly (e.g. unoccupied tenant suites, disabled WC taps, emergency showers).
- 06Test thermostatic mixing valves (TMVs) annually for failsafe shut-off operation to prevent scalding.
How often?
Monthly sentinel temperature checks · Quarterly shower descaling · 6-Monthly calorifier blowdown · Annual tank inspection · Review Legionella Risk Assessment at least biennially or after significant system modification.
Source: HSE Approved Code of Practice L8 (4th edition) & HSG274 Part 2.
What evidence should I hold?
Failure to manage Legionella risk violates Section 2, 3, or 4 of the Health and Safety at Work etc. Act 1974. HSE prosecutes corporate dutyholders following outbreaks with substantial criminal fines regardless of whether fatalities occurred.
Official Sources
HSE ACOP L8: Legionnaires disease. The control of legionella bacteria in water systems
HSG274 Part 2: The control of legionella bacteria in hot and cold water systems
EntireFM Practical Guidance
EntireFM recommends installing wireless LoRaWAN pipe temperature sensors on sentinel incoming mains and return loops. Continuous 15-minute telemetry eliminates manual logging labour and flags hot/cold crossover heating immediately.
EntireFM practical interpretation is separate from official statutory guidance. Always verify against primary legislation.