Do water system changes require a new Legionnaires’ risk assessment?

A water system change does not automatically mean that a completely new Legionnaires’ risk assessment is required. It does mean the existing assessment should be reviewed by a competent person to establish whether the system, its risks and its control measures have changed. If the original assessment no longer accurately describes the installation or how it is used, it must be updated or replaced.

This approach reflects the principles in the Health and Safety Executive’s Approved Code of Practice L8 and HSG274. The duty holder must keep the assessment suitable and sufficient, rather than treating it as a document that remains valid indefinitely after the first inspection. A change should therefore be considered as part of the organisation’s management-of-change process.

Changes that commonly require a formal review include:

• Installing, removing or resizing hot- or cold-water storage vessels
• Extending or altering distribution pipework
• Adding, relocating or removing taps, showers, safety showers or other outlets
• Changing water heaters, calorifiers, thermostatic mixing arrangements or temperature controls
• Introducing outlets that are used infrequently or creating sections of pipework with little or no flow
• Changing the building’s occupancy, operating pattern or water usage
• Bringing previously unused areas back into service
• Connecting a new installation to an existing water system or isolating part of the system

The significance of the change depends on how it affects conditions that allow Legionella to grow and spread. The reviewer should consider water temperatures, stagnation, storage capacity, flow patterns, accessible outlets, contamination risks and the effectiveness of existing control measures. A seemingly small alteration can be important if it creates a dead leg, reduces circulation or introduces an outlet that produces an aerosol.

Minor works may only require the existing assessment and schematic drawings to be amended. For example, replacing an outlet on a like-for-like basis may not alter the risk profile significantly, provided the work does not change temperatures, usage, flow or access for maintenance. The decision and the reasons for it should still be recorded; an assumption that a change is low risk is not a substitute for documented consideration.

A more extensive reassessment is normally appropriate where the change affects the fundamental design or operation of the system. This may include a major refurbishment, a new hot-water plant, substantial pipework alterations, changes to stored-water arrangements, a change in building use or a significant increase in the number or type of outlets. A reassessment may also be needed when several minor changes have accumulated and the original assessment no longer reflects the installation.

The review should normally take place before the modified system is put into routine use, where practicable. A competent assessor may examine the design information, commissioning records, schematic drawings and maintenance arrangements, then verify the installation on site. The review should identify any new control measures, responsible persons, monitoring points, remedial works or changes to written procedures.

Following alteration, control measures may need to be adjusted. Examples include revising temperature checks, adding outlets to flushing schedules, updating sampling locations, removing redundant pipework, improving insulation, correcting faulty thermostatic mixing valves or changing cleaning and disinfection requirements. Water testing can support an investigation, but test results alone do not replace a suitable risk assessment or effective ongoing control.

The assessment should be reviewed again if the completed work differs from the design, if commissioning identifies unexpected temperatures or flow problems, or if the system’s use changes later. Records should show what was altered, when it was completed, who reviewed the risk and which actions resulted. Keeping the assessment, drawings, asset information and monitoring records aligned helps the responsible person demonstrate that the system is being managed on current information.

Blue Fish Water Management Ltd can support businesses with Legionella risk assessments, compliance reviews, water testing, system monitoring and remedial recommendations. Its approach is to examine how a water system operates in practice, not simply whether a modification has been recorded, so that the level of review reflects the actual change and the risks it introduces.