BS 7592:2022 Sampling for Legionella Bacteria in Water Systems

BS 7592:2022 is aimed at commercial water systems - hot and cold-water distribution loops, tanks, calorifiers, cooling towers, spa pools and others where water can be stored, recirculated or aerosolised. It sets out how to take water, sediment or biofilm samples as part of your microbiological monitoring and how such sampling links into your overall water-safety strategy.

Why your sampling plan must have a clear rationale

One of the key principles of BS 7592:2022 is that Legionella sampling must be justified. That means you should not simply sample because “it seems like a good idea”. Instead you should be able to show why you are taking the sample: perhaps your risk-assessment has highlighted stagnation or an at-risk population now uses your facility; or perhaps your control scheme has recently failed. Without that justification, sampling becomes routine but not necessarily effective.

How it integrates into your duty-holder role

As the facilities manager or responsible person, you’re already aware of obligations under ACoP L8 and other HSE guidance. Sampling under BS 7592:2022 gives you a formal link between what your risk assessment identifies and how you verify that your controls work in practice. In other words: assessing risk → applying control measures → verifying via sampling.

Key updates in BS 7592:2022

Site-specific sampling plans

You now need a tailored sampling plan which is grounded in your site’s actual layout, usage and outcomes. You should identify sample points based on where legionella growth or aerosol exposure is most likely, not simply by choosing the most convenient outlets.

Storage-tank and cistern sampling amended

A common update is the advice that you no longer open potable water storage tanks purely to sample (‘dip sampling’). Instead, samples should be taken from a dedicated sample valve or the nearest outlet to the tank. The aim is to avoid introducing contamination during sampling and to capture water representative of what the user would draw.

Differentiation between routine and reactive sampling

The standard now clearly distinguishes routine monitoring (when systems are under control) from sampling triggered by incidents, changes in occupancy, system commissioning, or outbreaks. It includes appendices for outbreak investigations in multi-occupancy buildings and healthcare premises, so your sampling protocols should reflect the reason behind the sampling event.

Transport, handling and method requirements

Another practical change is emphasis on how samples are collected, labelled, transported and analysed: for example, ensuring samples are kept in appropriate temperature-controlled conditions, clear chain of custody is maintained, and laboratory methods are suitably sensitive.

Practical guidance for you as facilities manager

Linking your risk assessment and water-safety plan

Begin with your legionella risk assessment: this will identify vulnerable systems, storage tanks, loops, showers, taps, and any water outlets that might pose an exposure risk. From there your water-safety plan should include your sampling strategy. One way to explore this further is via our page on Legionella Risk Assessment Services.

Choosing when and where to sample

Routine sampling may not be necessary for simpler systems where controls are well evidenced and working. However you should consider sampling if:

• your control scheme shows signs of performance failure (e.g., temperature out-of-range, stagnation identified);

• occupancy or system use has changed (for example more frequent use, new at-risk users);

• you commission, recommission or alter the system; or

• you detect adverse microbiological or temperature trends. When selecting sample points, include the outlets most likely to capture risk (for example sentinel outlets, low-use loops, storage tank outlets) rather than defaulting to easy taps. If you’d like to read about how we support ongoing monitoring, check our Water Hygiene Monitoring Services.

Ensuring correct sampling method and lab procedure

In practice, aim for pre-flush samples from unmixed outlets when doing routine monitoring. Post-flush sampling may be appropriate for outlets presenting higher risk but bear in mind the interpretation becomes more complex. Make sure the laboratory is UKAS-accredited, chain of custody is clear, and results are interpreted in the context of your system and control measures.

Reviewing, interpreting and acting on results

Sampling is only useful if you act on what the results tell you. Any positive legionella result or unexpected finding demands investigation: look at flow, temperature, stagnation, biocide treatment and system design (including dead legs). Ensure your remedial plan is documented and integrated into your water safety plan.

How this fits into your compliance framework

Your sampling strategy under BS 7592:2022 should not stand alone. It must tie into other standards and guidance you already manage: for example ACoP L8 (Legionnaires’ disease: The control of legionella bacteria in water systems) and HSG 274 Part 2 (hot and cold water systems). Together they form your risk-based strategy: assess → control → monitor → review. When sampling is correctly justified, planned and executed, you strengthen your evidence-base for efficient compliance. Remember: robust temperature control, good system design, flushing and cleaning, and well-maintained records are all part of the story. Sampling provides the verification step.

Conclusion

BS 7592:2022 gives you a clearer, more rigorous framework for sampling legionella within water systems. For you as a facilities manager the key take-aways are: sampling only when justified, planning site-specific points, linking the work to your risk assessment and water-safety plan, and ensuring correct lab handling and interpretation. Sampling isn’t a tick-box—it is a vital verification tool in your overall water-hygiene regime. If you’d like to deepen your understanding of how to structure your monitoring regime, you can visit our Legionella Sampling Services section. And if you’d like to explore how your broader risk assessment framework should interact with sampling under BS 7592:2022, take a look at our blog Do I need a legionella risk assessment? | Titan Water.

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