Legionella Risk Assessment Checklist: 67 Conditions Based on HSG274

A thorough legionella risk assessment requires the assessor to evaluate every relevant risk condition in the water system. HSG274 Part 2 identifies specific conditions that contribute to legionella growth and transmission -- and L8Pro has organised these into 67 structured risk conditions across seven categories.

This checklist is designed to be used alongside your on-site assessment. It covers every condition you need to evaluate, grouped by system area.

How to use this checklist

For each condition, you should assess whether it applies to the system, whether existing controls are adequate, and what the residual risk is (using an ABC scale: A = adequately controlled, B = improvements recommended, C = immediate action required).

This checklist is based on HSG274 Part 2 (2024 edition) and ACOP L8. It covers hot and cold water systems in commercial and domestic buildings. Cooling towers and other specialist systems are outside its scope.

Category 1: Water system design and configuration

These conditions relate to the physical layout and design of the water system. Poor design is one of the most common root causes of legionella risk.

• 1.1 Is there a current, accurate schematic of the water system?
• 1.2 Are all parts of the system accessible for inspection and maintenance?
• 1.3 Are there dead legs or redundant pipework in the system?
• 1.4 Is the system made of materials that support biofilm growth?
• 1.5 Are there blind ends or capped-off connections?
• 1.6 Is the pipework adequately insulated to maintain temperature?
• 1.7a Is there evidence of scale or corrosion in the system?
• 1.7b Is there evidence of sediment or biological growth in the system?
• 1.8 Are expansion vessels fitted with backflow prevention?
• 1.9 Is there adequate separation between hot and cold pipework?
• 1.10 Are water storage tanks covered, insect-proof, and in good condition?

Category 2: Cold water system

Cold water systems must be maintained below 20 degrees C to prevent legionella growth. These conditions evaluate whether the cold water supply is adequately controlled.

• 2.1 Is the cold water storage tank sited to minimise temperature gain?
• 2.2 Is cold water stored below 20 degrees C?
• 2.3 Is the cold water distribution temperature below 20 degrees C within 2 minutes of running?
• 2.4 Is the incoming mains supply adequate for the building's needs?
• 2.5 Are there any point-of-use filters or treatment on the cold water supply?
• 2.6 Is the cold water tank sized appropriately (not oversized)?
• 2.7 Is there evidence of stagnation in cold water outlets?
• 2.8 Are cold water pipes routed away from heat sources?

Category 3: Hot water system (generation)

These conditions relate to how hot water is generated and stored. Calorifiers, water heaters, and cylinders must maintain temperatures that prevent legionella growth.

• 3.1 Is hot water stored at 60 degrees C or above?
• 3.2 Is the calorifier or water heater in good condition?
• 3.3 Is there a functioning thermostat on the storage vessel?
• 3.4 Is the calorifier drained and inspected on a regular basis?
• 3.5 Are there multiple storage vessels, and are all in use?
• 3.6 Is the bottom drain valve accessible and functional?
• 3.7 Is there a shunt pump or return circuit to maintain temperature?
• 3.8 Is the hot water generation capacity adequate for the building?

Category 4: Hot water system (distribution)

Distribution temperature is critical. Hot water must reach outlets at 50 degrees C or above within one minute of running.

• 4.1 Is hot water distributed at 50 degrees C or above?
• 4.2 Do all outlets reach 50 degrees C within one minute of running?
• 4.3 Is there a hot water return circuit, and is it functioning?
• 4.4 Are thermostatic mixing valves (TMVs) fitted where required?
• 4.5 Are TMVs maintained and serviced regularly?
• 4.6 Is the hot water pipework insulated?
• 4.7 Are there any long runs of pipework that could allow temperature drop?
• 4.8 Is there evidence of temperature fluctuation at distant outlets?

Category 5: Outlets and use patterns

Infrequently used outlets are a significant risk factor. Stagnant water at the right temperature is the ideal environment for legionella.

• 5.1 Are all outlets in regular use (at least weekly)?
• 5.2 Is there a flushing regime for infrequently used outlets?
• 5.3 Are showers fitted with removable and cleanable heads?
• 5.4 Is there evidence of biofilm or scale on shower heads?
• 5.5 Are taps fitted with aerators, and are they clean?
• 5.6 Are there any spray-generating outlets (hoses, spray taps)?
• 5.7 Are there any outlets in areas used by vulnerable persons?
• 5.8 Is there a log of all outlets with their use frequency?
• 5.9 Are there any seasonal or intermittently used areas?
• 5.10 Is there a recommissioning procedure for outlets returned to use?

Category 6: Water treatment and monitoring

Water treatment and temperature monitoring are the ongoing controls that keep legionella risk managed after the assessment.

• 6.1 Is there a water treatment regime in place?
• 6.2 Is the treatment method appropriate for the system type?
• 6.3 Are treatment chemical levels monitored and recorded?
• 6.4 Is temperature monitoring carried out at sentinel outlets?
• 6.5 Are monitoring records maintained and reviewed?
• 6.6 Is there a programme of legionella sampling?
• 6.7 Are sample results reviewed and acted upon?
• 6.8 Is the responsible person reviewing monitoring data regularly?
• 6.9 Is there a procedure for responding to adverse results?
• 6.10 Are annual reviews of the monitoring programme carried out?

Category 7: Management and documentation

These conditions assess whether the organisational framework for legionella control is adequate.

• 7.1 Is there a named responsible person for legionella management?
• 7.2 Has the responsible person received adequate training?
• 7.3 Is there a written scheme for controlling legionella risk?
• 7.4 Are records of maintenance and monitoring kept and accessible?
• 7.5 Is there a procedure for reporting and investigating adverse events?
• 7.6 Are contractors and third parties made aware of legionella controls?
• 7.7 Is the risk assessment reviewed at appropriate intervals?
• 7.8 Is there a communication plan for notifying relevant parties of risk changes?
• 7.9 Are all building modifications assessed for impact on the water system?
• 7.10 Is there a scalding risk assessment where TMVs are fitted?
• 7.11 Is there an incident response plan for suspected legionella cases?

Using the ABC risk rating

For each condition, assign a risk rating:

• A -- Adequately controlled: The condition is met and existing controls are sufficient. No action required beyond ongoing monitoring.
• B -- Improvements recommended: The condition is partially met or controls could be improved. Remedial actions should be planned and implemented within a reasonable timeframe.
• C -- Immediate action required: The condition presents a significant risk that must be addressed urgently. The duty holder should be notified immediately and remedial action taken without delay.

L8Pro automates this entire checklist, guiding assessors through each condition on-site and generating a compliant PDF report with all findings, risk ratings, and recommendations.

Key points to remember

• Every condition should be assessed -- even if you mark it as not applicable, record why
• Take photographs of key findings to support your report
• Record the temperature at sentinel outlets during your visit
• Note the condition and location of water storage tanks, calorifiers, and any visible pipework
• Check the maintenance log and monitoring records -- their absence is itself a risk factor
• Always date and sign your assessment