Legionella Inspection: What to Expect During a Professional Assessment

If you have booked a professional legionella risk assessment for the first time, you may not know what to expect. This guide explains what happens during a typical assessment visit, what the assessor must cover to meet ACoP L8 requirements, and what documentation you should receive afterwards.

Before the visit: what to have ready

A professional assessor will want to understand the water system before arriving and will use information you provide to scope the inspection. Useful documents to have available:

• Building plans or drawings showing the layout and floor plan, if you have them
• Any previous legionella assessments — the new assessor will want to compare findings
• Maintenance records — boiler service history, plumber callout logs, any known system problems
• A list of tenants or building occupants — particularly any who may be in a higher-risk group (elderly, immunocompromised)
• Utility room, tank room, or plant room access — the assessor needs physical access to storage tanks, boiler rooms, and mechanical plant

For a straightforward residential property, you may not have any of this formally documented. That is fine — the assessor will carry out a site survey as the primary evidence-gathering exercise.

What happens during the inspection visit

1. System walkthrough and inventory

The assessor will walk through the entire building and document the water system. Under HSE's risk assessment guidance, this includes:

• All water sources — incoming mains, any private supply
• Storage — cold water tanks (location, capacity, condition), hot water cylinders (size, thermostat setting)
• Distribution — pipework layout, insulation, any known dead legs or redundant branches
• Outlets — every tap, shower, bath, toilet cistern, and other water-using fitting, by location

For a typical flat or house, this walkthrough takes 20–40 minutes. For a large commercial building or HMO, it takes longer — the assessor may spend an hour or more mapping the full system.

2. Temperature measurements

Temperature is the primary control parameter for legionella risk. The assessor will measure:

• Hot water storage temperature — the cylinder thermostat reading and a surface or probe measurement
• Hot water at sentinel outlets — the nearest and furthest outlets from the heat source. Both should reach 50°C or above within one minute of running
• Cold water at sentinel outlets — after two minutes of running, the temperature should be below 20°C

A reading outside these thresholds does not necessarily mean the property is non-compliant — but it will be identified as a finding requiring investigation or corrective action.

The assessor carries a calibrated digital thermometer. They will run the taps and record actual temperatures, not just check thermostat settings. This is an important distinction: a thermostat set to 60°C does not guarantee that water is actually reaching 60°C throughout the system.

3. Hazard identification

Based on the system walkthrough and temperature readings, the assessor identifies specific hazards. HSE specifies that the assessment must examine conditions including:

• Water temperatures in all or some parts of the system falling between 20°C and 45°C (the legionella growth zone)
• Water that is stored or recirculated in the system
• Sources of nutrients including rust, sludge, scale, organic matter, and biofilm
• Aerosol-generating outlets — "whether they can be dispersed over a wide area, for example showers and aerosols from cooling towers"

They will also note:

• Dead legs and infrequently used outlets
• Poorly insulated cold water pipes running near heat sources
• Showerheads showing visible scale or biofilm
• Tank condition (lid, insulation, any signs of contamination)

4. Occupant risk assessment

The assessor will ask about the building's occupants and identify anyone who may be at higher risk if they were to contract Legionnaires' disease. Higher-risk groups include elderly residents, people who are immunocompromised, and those with chronic respiratory conditions.

For most residential lets, this is a brief discussion. For care homes, sheltered housing, or any setting with medically vulnerable occupants, it becomes a more significant part of the assessment.

5. Discussion of control measures and recommendations

Towards the end of the visit, the assessor will typically discuss their initial findings with you and outline what control measures are already adequate and what needs attention. This is an opportunity to ask questions.

Common findings on residential properties include:

• Cylinder thermostat set below 60°C (usually set low to save energy or reduce scald risk)
• Cold pipes running through warm spaces gaining heat
• Showerheads overdue for descaling
• Dead legs from old plumbing that was not removed when the system was modified
• No record of monitoring from previous years

None of these are unusual. The purpose of the assessment is to identify them so they can be managed.

How long does a professional assessment take?

Property type	Typical site visit duration
Studio or one-bedroom flat (combi boiler)	30–45 minutes
Two to three-bed house with stored cylinder	45–60 minutes
HMO (up to 6 beds)	60–90 minutes
Large HMO or small commercial building	90 minutes – 2.5 hours
Care home or complex commercial building	Half day or more

The written report usually follows within 5–10 working days of the visit.

What documentation you should receive

A compliant legionella risk assessment is a written document, not just a verbal report. Under ACoP L8, the document must include:

1. A description of the water system — inventory, layout, components
2. Identified hazards with their likelihood and severity rated
3. The people at risk and any higher-risk groups identified
4. Control measures in place and any recommended corrective actions
5. A monitoring schedule — what checks are needed, at what frequency
6. The name of the responsible person accountable for implementing the scheme
7. A statement on review arrangements — the assessment must be reviewed regularly and whenever there is reason to believe it is no longer valid (for example after system changes or a monitoring failure)

If the document you receive does not include all of these, ask the assessor why. A one-page summary sheet is not a compliant ACoP L8 risk assessment — regardless of what it is labelled.

The report should also include the temperature readings taken during the visit, listed by outlet with the recorded value.

What happens after the assessment

After the visit and report, you have two categories of responsibility:

Corrective actions: If the report identified findings — low cylinder temperature, dead legs, scale in showerheads — these need to be remediated. The report should specify which are urgent and which can be addressed during routine maintenance.

Ongoing monitoring: The risk assessment is not a one-time tick. After the initial assessment, you must carry out and record monthly temperature checks, weekly flushing of unused outlets, and quarterly showerhead maintenance. See our legionella checks for landlords guide for the full ongoing schedule.

Practical takeaway

A professional legionella inspection is primarily a structured site survey followed by a written document. The assessor maps your water system, takes temperature readings at key outlets, identifies hazards, and recommends control measures. They will spend between 30 minutes and several hours on site depending on property size and complexity.

The outcome is a written ACoP L8-compliant risk assessment document — not a certificate, not a brief form — that records what was found and what needs to happen next.

For standard residential properties, landlords can carry out this assessment themselves without hiring a professional. If you want to understand what a self-assessment involves, see our guide to self-assessment for landlords.

This guide covers what to expect during a professional legionella risk assessment visit in the UK. This is general guidance only — for complex systems, consult a competent person as defined by ACoP L8.

Sources

• HSE — ACoP L8: Legionnaires' disease
• HSE — Identify and assess sources of risk
• HSE — Legionella and landlords' responsibilities