The HSE have released an update to HSG 274 Part 1 The control of Legionella bacteria in evaporative cooling systems. 


Part 1 has been updated to provide improved guidance on a number of areas when managing the legionella risk presented by evaporative cooling systems. These changes include:

§  further information on DPD No 1 testing methodology 

§  the effect that cooling water pH has on the efficacy of halogen-based biocides such as chlorine and bromine

Many organisations rely on this test to ensure correct dosing of their systems. The pH correction of free-halogen test results is a vital part in ensuring you have sufficient biocide in your system to prevent the growth of legionella. Check your most recent results and ensure they are pH corrected.

The updated document, second edition, is available for FREE download from the HSE website and has been supported by the chair of Water Management Society.  


We will continue to keep you updated as further changes are made to parts 2 and 3.