When should water hygiene controls be reviewed after a system change?

The controls should be reviewed at defined decision points: when the proposed change is assessed, when the modified system is commissioned, once operating conditions have stabilised, and whenever monitoring or sampling shows that the control strategy may no longer be effective. The review should be proportionate to the change and recorded as part of the water hygiene management system.

Review before work begins. The responsible person should establish whether the change could alter the conditions that support Legionella growth or exposure. Relevant changes may include alterations to hot or cold water pipework, storage tanks, calorifiers, pumps, valves, outlets, thermostatic mixing arrangements, water treatment equipment, insulation, control settings or system use. Changes in occupancy, building function or periods of reduced use can also affect the risk, even where the physical installation is unchanged.

This initial review should identify affected assets, areas that may become low-use or stagnant, changes to flow and temperature, new points of exposure, access requirements and any temporary arrangements needed during the work. The schematic, asset register and written control scheme should be updated or marked for revision so that the post-change checks cover the whole affected section rather than only the newly installed item.

Review at handover and commissioning. The completed work should not be treated as fully controlled simply because installation is finished. Commissioning information should demonstrate that the system has been installed, cleaned or disinfected where required, configured correctly and returned to an operating condition that matches the water hygiene requirements. The review should consider:

• whether dead legs, redundant branches or inaccessible sections have been introduced;
• whether storage and distribution arrangements still allow suitable circulation and turnover;
• whether hot and cold water temperatures can be controlled and monitored at representative points;
• whether outlets, showers and thermostatic mixing valves are correctly identified and accessible for inspection;
• whether strainers, filters, tanks, calorifiers, pumps and treatment equipment are included in the maintenance schedule; and
• whether operating instructions, isolation points and responsibilities have been passed to the people managing the system.

Any flushing, cleaning, disinfection or remedial work should be supported by appropriate records. These may include commissioning sheets, disinfection certificates, temperature results, photographs, updated drawings, test results and information about materials or equipment installed. The purpose is to show what was done and provide a reliable baseline for subsequent monitoring.

Review after the system has stabilised. A further review is needed after the modified arrangement has been used under normal operating conditions for long enough to produce meaningful monitoring information. The reviewer should compare actual temperatures, flow, usage, flushing results and other control data with the assumptions made during design and commissioning. Where sampling forms part of the control programme, the results should be interpreted alongside the operational evidence rather than considered in isolation.

This stage can identify problems that are not apparent during handover. For example, a newly altered branch may have poor turnover, a remote outlet may be difficult to maintain at the intended temperature, or a change in demand may leave storage capacity or circulation arrangements unsuitable. If results or observations indicate loss of control, the risk assessment and control measures should be revised rather than waiting for the next routine review.

Review when the change is temporary. Temporary bypasses, out-of-service plant, emergency repairs, decanting arrangements and partially occupied buildings can alter the risk for as long as they remain in place. These arrangements should have a defined review point, clear ownership and a plan for returning the system to its intended configuration. When the temporary measure ends, the affected controls, records and monitoring points should be checked again.

Review following evidence of changed performance. A formal review should also be triggered by repeated temperature failures, unusual microbiological results, inadequate flushing, changes in water usage, equipment failure, complaints relating to water quality, or evidence that planned tasks are not being completed. The same applies where a building changes use, an area is reopened after prolonged closure, or responsibility for the system moves to another organisation.

In practical terms, the review should answer four questions: what has changed, how has the risk changed, which controls now manage that risk, and what evidence confirms that those controls work? The outcome should state any additional monitoring, sampling, cleaning, flushing, maintenance, training or remedial work required, together with responsible persons and target dates.

For complex systems or significant alterations, an independent water hygiene specialist can help interpret the design and operational evidence, assess whether the revised arrangements remain proportionate, and identify gaps between the installed system and its documented controls. Blue Fish Water Management Ltd provides risk assessments, water testing, compliance audits, system monitoring and remedial support for organisations reviewing water hygiene controls after system changes.