A Guide to Professional Legionella Testing

Edited 26/08/25

Legionella is a potentially harmful bacteria that can thrive in water systems if not properly managed. Ensuring the safety of your water supply is not just good practice—it’s a legal requirement. Carrying out regular Legionella risk assessments, monitoring, and control measures helps identify any issues early, protect occupants, and maintain compliance with health and safety regulations.

Risk assessments, monitoring and assessment programmes help identify the presence of harmful Legionella bacteria and ensure that any issues are quickly resolved. It is a legal requirement that legionella risk assessments are carried out on water systems by a qualified assessor in order to ensure that any required steps are taken to avoid issues with this harmful bacteria.

Carrying out regular risk assessments and monitoring for legionella is useful to ensure that there are no issues developing. One method used to assess issues with legionella on a site is microbiological sampling. This can provide detailed information on the water quality throughout different water systems on a site and allow for accurate risk assessments and monitoring of any issues.

Read more for some further information on the ways in which water treatment engineers can identify and remove legionella from water systems.



Legionella Risk Assessment

Landlords and site managers are legally required to carry out Legionella risk assessments in both domestic and commercial properties. This requirement is outlined in the HSE Approved Code of Practice (ACOP) L8. A proper Legionella risk assessment is not a one-off task; it is an ongoing process designed to ensure that the site’s water systems remain safe and that any issues are addressed promptly.

Implementing a structured risk assessment programme helps prevent Legionella proliferation, protects building occupants, and ensures compliance with health and safety regulations.

Microbiological Sampling

Microbiological sampling can be used to provide an accurate picture of the bacterial profile of a water system. When carrying out microbiological sampling there will typically be specific harmful bacteria that are being checked for with one example being Legionella. If Legionella is identified there are a range of cleaning methods that can be utilised as a part of a broader approach to resolving issues in a site’s water system. Some of these methods include water tank chlorination, silver-stabilised Hydrogen-Peroxide and thermal disinfection.

When your water tank is chlorinated, you will be provided with a chlorination certificate. This document will contain detailed information about the chlorination procedure, including the date and time of the chlorination, the type and concentration of disinfectant used, and the duration of the chlorination process.

Water Tank Cleaning

It is important that water tank cleaning is carried out by specialist water treatment engineers experienced in resolving issues with Legionella. In addition to removing harmful bacteria from a site’s water system, these cleaning methods can also resolve a range of other issues including removing biofilms, resolving issues with corrosion and preventing the build-up of sediment.

If Legionella is identified in your water system, a water treatment engineer will be able to identify the best approach to resolving this issue and preventing any future issues.

How we can help with legionella control.

Our experienced water treatment engineers at H2O Comply Limited specialise in providing comprehensive Legionella risk assessments, monitoring, and inspection programmes for water systems of all types, whether domestic, commercial, or industrial. We work closely with clients to identify potential risks, implement effective control measures, and ensure ongoing compliance with legal requirements. In addition to Legionella management, we offer a wide range of water treatment and consultancy services, including water tank cleaning, microbiological sampling, and bespoke water hygiene programmes tailored to your site’s specific needs.

Our team is committed to helping you maintain safe, healthy water systems while providing clear guidance, detailed reports, and practical solutions for preventing and resolving Legionella issues. To learn more about our services and how we can help safeguard your water systems, get in touch today or email us at enquiries@h2ocomply.co.uk.