What Does a Legionella Risk Assessment Include?

What Does a Legionella Risk Assessment Involve?

If you have been told you need a legionella risk assessment but are not sure what to expect, this guide explains exactly what a professional assessment covers, what documentation you will receive, and why each element matters for your legal compliance.

Understanding what is involved will help you prepare for the assessment visit and ensure you get maximum value from the process.

The Site Visit

Every legionella risk assessment begins with a physical site visit from a qualified assessor. During this visit, the assessor will inspect every aspect of your water systems to identify potential risk areas and assess how well your current arrangements manage those risks.

The assessor will need access to all water-related areas of the property, including plant rooms, loft spaces (for cold water storage tanks), all bathrooms and shower rooms, kitchens, and any utility areas with water connections. The more access you can provide, the more thorough and accurate the assessment will be.

Temperature Testing

One of the most important elements of any legionella risk assessment is temperature profiling. Legionella bacteria multiply rapidly in water held between 20°C and 45°C, so checking that your hot and cold water is maintained at safe temperatures is a fundamental part of the process.

The assessor will test water temperatures at all sentinel outlets — typically the first and last outlets on each hot and cold water loop — and at the hot water storage cylinder or calorifier if present. Hot water should reach 50°C at the outlet within one minute. Cold water should be below 20°C within two minutes of running.

Any outlets that fail these temperature thresholds will be flagged in the report, along with recommended actions to bring them into compliance.

Water System Survey and Schematic Drawing

The assessor will document the layout of your entire water system, identifying all components including storage tanks, cylinders, pipework, outlets, showers, thermostatic mixing valves, and any dead legs or rarely used sections. For commercial premises and HMOs, a non-technical schematic drawing of the water system is produced as part of the assessment. This drawing forms part of your ongoing compliance documentation.

Risk Identification and Assessment

Based on the site inspection and temperature data, the assessor will evaluate the risk posed by each element of your water system. Risk factors they look for include stagnant water sections, scale or biofilm build-up in pipework and showerheads, inadequate insulation on cold water pipes running near heat sources, infrequently used outlets, and any redundant or dead-end pipework.

Each risk is rated by severity and likelihood, and the report explains what actions are needed to reduce or eliminate the risk.

The Written Risk Assessment Report

Following the site visit, you will receive a comprehensive written report. This document includes the findings of the assessment, risk ratings for each identified issue, a list of recommended control measures with priority actions, and evidence of the temperature checks carried out.

The report is your primary compliance document. It demonstrates that you have fulfilled your duty under ACoP L8 to carry out a suitable and sufficient assessment. Keep it securely — you may need to produce it for the HSE, your local council, an insurer, or a letting agent.

The Written Scheme of Control

Every risk assessment should be accompanied by a Written Scheme of Control — a document that sets out exactly how you will manage your water systems going forward. This includes the monitoring regime (what checks to carry out and how often), the person responsible for each task, temperature control targets, and the schedule for showerhead disinfection, tank inspection, and other routine maintenance.

The Written Scheme is a live document that should be reviewed whenever the risk assessment is reviewed or whenever significant changes are made to the water system.

What Happens After the Assessment?

Once you receive your report, you should prioritise any actions rated as high risk and address them promptly. Lower-priority items should be scheduled and completed within a reasonable timeframe. Your Written Scheme of Control provides the framework for ongoing management until the next formal review.

Get in touch