Legionella bacteria can grow in man-made water systems when temperature, stagnation and system condition allow growth. If people inhale contaminated water droplets, they can develop Legionnaires’ disease, which can cause serious illness.
UK law does not require routine sampling in every building or every water system. Duty holders still need to assess risk, put suitable controls in place, monitor those controls and keep records. When a legionella risk assessment or written control scheme identifies sampling as necessary, missed testing can leave a gap in the evidence used to manage the system.
This blog explains what can happen when duty holders do not complete required sampling, why HSE guidance takes a risk-based approach and how planned monitoring can help organisations manage future compliance with more confidence.
Is Legionella Testing Always Required?
Legionella testing is not a blanket requirement for every commercial water system. HSE guidance focuses on assessing the risk from the system and then applying suitable control measures.
For many hot and cold-water systems, temperature monitoring, flushing, inspection, cleaning and maintenance provide the main control measures. Sampling may form part of the control scheme when the risk assessment shows a need for microbiological evidence. This can apply when temperature control does not provide enough assurance, when the system serves higher-risk people, when previous results or incidents raise concerns, or when the control scheme requires periodic sampling.
The duty holder should avoid treating sampling as a stand-alone activity. A clear control scheme should explain what checks need completing, who will complete them, how the organisation will record results and what action staff should take when results show a concern.
What Happens If Duty Holders Miss Required Legionella Testing?
If the written scheme requires legionella testing and the organisation does not complete it, the duty holder loses a planned check on system control. That gap can affect decision-making.
Legionella bacteria do not change the appearance of a water system in a way that a facilities team can reliably see. A shower, tap or storage vessel can appear normal while conditions inside the system support bacterial growth. Stagnant water, poor temperature control, scale, sediment and biofilm can all make control harder.
Missed sampling can also delay action. If a sample would have identified a concern, the site may continue with the same flushing regime, maintenance plan or temperature control approach. Over time, that can allow the issue to become harder to manage.
The main practical problem is uncertainty. The organisation may not know if the control scheme still matches the current risk. That makes it harder to plan remedial work, explain decisions internally and demonstrate that the site has followed its own arrangements.
Can Lack of Testing Increase Health Risk?
A missed sample does not automatically mean people will become ill. The risk depends on the system, the level of control, the people exposed and the way water droplets can form.
If a risk assessment has already identified sampling as necessary, missed testing can reduce the organisation’s ability to spot bacterial growth early. That matters in buildings with showers, healthcare environments, care settings, leisure facilities, complex hot and cold water systems or other equipment that can create aerosols.
Legionnaires’ disease can affect anyone, although some people face greater risk due to age, health conditions or other factors. Good management aims to control the conditions that allow legionella bacteria to grow and spread. Testing, when required, gives the responsible person another source of information to support that work.
Could Failure to Test Lead to Enforcement Action?
Regulators do not only look at testing results. They look at how the duty holder has assessed risk and managed the control scheme.
HSE guidance says duty holders must identify and assess sources of risk, manage risks, prevent or control risks, keep suitable records and carry out relevant duties. ACoP L8 also gives guidance on risk assessment, the role of the responsible person, control schemes, review of control measures and responsibilities linked to water systems.
If an organisation’s own risk assessment or written scheme identifies sampling as necessary, missing that activity can raise questions. The organisation may need to explain why it did not follow the scheme, how it maintained control and what evidence supports its decisions.
Enforcement action depends on the facts of the site and any investigation. A missing test does not create the same position in every case. Still, poor records, outdated assessments and uncompleted control measures can weaken the duty holder’s position if a regulator reviews the arrangements.
Why Records Matter for Future Compliance
Good records help facilities teams manage risk with less confusion. They show what the organisation planned, what staff completed, what the results showed and how the responsible person responded.
Testing results can help the organisation identify patterns across a building or estate. They can show if a remedial action worked, if one part of the system needs closer attention or if the control scheme needs updating. Clear records also support handovers when staff change or when contractors take on planned maintenance.
This gives the business a practical benefit. The team can plan work in advance, budget for remedial action with better information and respond to audit questions without relying on memory. Over time, that makes legionella management easier to control.
How Should Duty Holders Manage Testing Going Forward?
Duty holders should start with the current risk assessment. If it no longer reflects the building, occupancy or water system, they should arrange a review. Changes in use, periods of low occupancy, refurbishment work and new outlets can all affect water hygiene controls.
The written scheme should then set out the monitoring activities for that system. It should make sampling requirements clear, including the purpose of sampling and the action process after results arrive. Competent people should review findings and decide if further investigation, cleaning, disinfection or remedial work needs completing.
A planned approach helps the site avoid reactive management. It gives the responsible person a clearer route from risk assessment to monitoring, from results to action and from action to review.
Speak to Safety First Group About Legionella Compliance
Legionella testing is not required in every case, but it becomes important when a risk assessment or control scheme identifies a need for it. If duty holders miss required sampling, they may lose evidence, delay corrective action and find it harder to demonstrate control.
We support organisations with legionella risk assessments, water sampling, monitoring programmes and ongoing compliance advice. Contact our team to review your current arrangements and agree the most suitable next step for your water systems.
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