Who decides the frequency of a legionella risk assessment?

The frequency of a legionella risk assessment is decided by the responsible person, using competent professional advice and the conditions identified within the water system. There is no single review interval that applies to every building. The decision must be justifiable, recorded and revised when the risk profile changes.

Who is the responsible person? The responsible person is the individual or organisation with control of the premises, water system or maintenance arrangements. Depending on the setting, this may be an employer, building owner, landlord, facilities manager or managing agent. In shared or complex premises, more than one duty holder may have responsibilities, and they must establish clearly who controls each part of the system.

Appointing a contractor or risk assessor does not remove the responsible person's legal accountability. The responsible person must ensure that the assessment is commissioned, that its findings are understood, and that necessary control measures are put into practice. They should also challenge an interval that does not appear proportionate to the building's use, system complexity or level of risk.

What does the competent assessor decide? A competent assessor examines the system and recommends a suitable review frequency. This recommendation should arise from the evidence gathered during the assessment rather than from a standard date applied automatically. The assessor considers the design and condition of the system, how water is stored and distributed, temperature control, outlets and usage patterns, maintenance arrangements, and the vulnerability of people who may be exposed.

The assessor may recommend a shorter interval where there are significant risks, incomplete records, poor temperature control, infrequently used outlets, complex distribution systems or uncertainty about the system's condition. A longer interval may be reasonable where the system is well understood, stable, effectively controlled and supported by reliable monitoring records. The recommendation should explain the reasoning, not simply state a date.

What guidance applies? The Health and Safety Executive's Approved Code of Practice L8 and associated guidance provide the framework for managing legionella risks in relevant water systems. They do not create one universal reassessment frequency for all premises. Instead, they support a risk-based approach in which the responsible person can demonstrate why the chosen interval is suitable.

This is different from routine control work. Temperature checks, flushing, inspection, cleaning, disinfection, sampling and other monitoring activities may be required at intervals set by the control scheme. Those activities do not automatically replace a formal risk assessment review. The assessment should confirm whether the control scheme remains appropriate and whether monitoring results indicate that the risk has changed.

How the decision should be made

1. Identify the person or people with control of the premises and water systems.
2. Appoint an assessor with suitable knowledge, training and experience where an independent assessment is needed.
3. Review the current assessment, schematic information, monitoring records, maintenance reports and any outstanding remedial actions.
4. Consider whether the system, building use, occupancy or exposed population has changed.
5. Agree a review interval that reflects the documented risk and any relevant professional recommendations.
6. Record the decision, its rationale, the person responsible for arranging the next review and any interim controls required.

A responsible person should not rely on the date alone. The recorded decision should identify what was considered, who provided the advice, which actions remain open and what events would trigger an earlier review. This makes it easier for managers, auditors and enforcement authorities to see that the interval was actively assessed rather than allowed to continue by default.

When the parties disagree If an assessor recommends more frequent reviews than the organisation expected, the responsible person should ask for the technical reasoning and address the underlying risk rather than simply selecting a later date. Conversely, an assessor should be able to explain why a longer interval remains appropriate and what evidence supports that conclusion. For a multi-occupancy building, the relevant parties may need to share information and agree a coordinated approach.

The frequency should be reconsidered after alterations, changes in occupancy or use, prolonged periods of low water use, changes to management or maintenance arrangements, contamination incidents, control failures, or evidence that existing measures are ineffective. A review may also be needed when the original assessment is incomplete or no longer reflects the installed system.

In practical terms, the responsible person makes and owns the decision, while a competent assessor supplies the technical judgement needed to make it defensible. The final record should show both the chosen frequency and the circumstances that would require the assessment to be brought forward.