Practical advice on controlling legionella bacteria in water systems
Health and safety information on managing and controlling legionella bacteria in water systems has been updated and clarified.
The Health and Safety Executive (HSE) has revised the Legionnaires’ disease Approved Code of Practice (ACOP) (L8), removing the technical guidance, which will be published separately online. The L8 ACOP was one of several identified for review and revision, consolidation or withdrawal in line with a recommendation by Professor Ragnar Löfstedt in his report ‘Reclaiming health and safety for all’.
The 4th edition L8 ACOP, which is aimed at dutyholders including employers, those in control of premises and people with health and safety responsibilities for others, provides greater clarity for dutyholders as to what constitutes legal requirements and what is guidance, and where possible we have simplified terminology and placed greater emphasis on proportionality in low risk scenarios. However, changes to ACOPs have not altered the legal responsibilities to protect workers' health and safety.
The revised edition was subject to consultation and received HSE Board and ministerial approval. It includes information on identifying and assessing sources of risk, preparing a scheme to prevent or control risk, implementing, managing and monitoring precautions, keeping records of precautions and appointing a competent person with sufficient authority and knowledge of the installation to help take measures needed to comply with the law.

The 4th edition L8 ACOP is now available on the HSE website at:

The review also enabled HSE to update technical guidance to incorporate technological advancements and separate it from general guidance on the regulations, making it available separately on our website. The revised guidance, HSG274, is available online in three parts on the HSE website at: and includes links to:
HSG274 Part 1: The control of legionella bacteria in evaporative systems
HSG274 Part 2: The control of legionella bacteria in hot and cold water systems
This section is interim guidance only and is an extract from the 3rd edition L8 ACOP until the review of the revised section is complete. Once Part 2 is finalised, this will be published online and a hard copy printed version of HSG274 comprising the three sections will also be made available.
HSG274 Part 3: The control of legionella bacteria in other risk systems