Legionella Control & ACoP L8 Explained
Controlling legionella in building water systems is a legal duty. This guide explains what ACoP L8 and HSG274 require, the main control measures, and the records you need.
In short
ACoP L8 is the HSE's Approved Code of Practice for controlling legionella bacteria in water systems. With the technical guidance HSG274, it sets out the duty to assess and manage the risk of legionnaires' disease through a written control scheme, monitoring, and record-keeping.
The legal duty
Legionella control sits under the Health and Safety at Work Act and the Control of Substances Hazardous to Health Regulations, with ACoP L8 setting the approved code of practice and HSG274 providing the technical detail. The dutyholder must identify and assess the risk, prepare a written scheme of control, appoint responsible people, and ensure controls are implemented, monitored, and recorded. The duty applies to most non-domestic water systems — from cold water storage tanks and calorifiers to cooling towers, showers, and TMVs.
Key control measures
Legionella thrives in stagnant water between roughly 20°C and 45°C. The control measures all aim to deny it those conditions: keeping cold water cold, hot water hot, water moving, and systems clean. The legionella risk assessment determines which measures apply and how often each is checked.
- Keep cold water stored and distributed below 20°C
- Keep hot water stored at 60°C and distributed at 50°C+ (with scald control)
- Flush little-used outlets weekly to prevent stagnation
- Monitor sentinel outlet temperatures monthly
- Inspect and clean cold water tanks and calorifiers
- Maintain TMVs to balance scald and legionella risk
- Remove dead legs and redundant pipework
Monitoring and records
Much of legionella compliance is about consistent monitoring and the records that prove it: temperature logs, tank inspections, flushing records, TMV servicing, and remedial actions. These records demonstrate the written scheme is being followed and are the evidence the HSE or an insurer will ask for. Because the data accumulates across many outlets and assets over time, keeping it organised and retrievable is part of staying compliant — and being able to search the water risk assessment and logbook quickly makes audits and reviews far less painful.
Related maintenance checklists
Frequently asked questions
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