What Happens During A Commercial Property Legionella Risk Assessment?

Part of: Legionella Risk Assessments for UK Commercial Property: A Complete Guide for Dutyholders

If you are responsible for a workplace, managed building, retail unit, healthcare setting, school, hotel, industrial site or mixed-use premises, the commercial property legionella risk assessment process is there to identify where water systems could support Legionella growth and how exposure to aerosol could affect staff, visitors, residents or contractors. It is not a paperwork exercise. A competent assessment is meant to show how your water systems actually operate, where control weaknesses sit, and what action is sensible for that specific property.

For most dutyholders, the main question is straightforward: what actually happens during the assessment, and what will the assessor need from you? In practical terms, a Legionella risk assessment for commercial premises usually starts with a review of the building, its water systems, its occupancy and any existing control records. That is followed by a site inspection, system tracing, discussions with the person in control of the premises, and a written report setting out risks, priorities and recommended Legionella control measures.

The detail matters because weak system knowledge, poor temperature control, deadlegs, low turnover outlets, inadequate monitoring and unmanaged changes to pipework are common reasons risk builds up unnoticed. A proper commercial water system risk assessment should leave the dutyholder with a clear picture of what is in place, what is missing, and what needs to happen next.

What The commercial property legionella risk assessment process Is Designed To Do

The purpose of the assessment is to establish whether the water systems in a commercial property present a reasonably foreseeable risk from Legionella, and whether existing precautions are suitable. In the UK, the legal framework sits broadly under health and safety law, while Legionella regulations and guidance are commonly interpreted through ACOP L8 and HSG274. Those documents do not remove the need for judgement. They support a risk-based approach, which means the assessor has to understand the premises, the systems and the people who may be exposed.

A well-executed assessment is designed to answer several practical questions:

• What water systems are present and how are they configured?
• Where could water stagnate, sit in the Legionella growth range, or generate aerosol?
• Who could be exposed, and are any occupants more vulnerable?
• What control measures are already in place, and are they working in reality rather than only on paper?
• What remedial work, monitoring or management action is needed?

That matters because the risk is not spread evenly across every property or every system. A modern office with limited domestic water services will not present the same profile as a hotel, care facility or leisure site with showers, spa areas, calorifiers, storage vessels and complex secondary returns. The process is meant to separate lower-risk features from the parts of the system that deserve attention.

It also gives the dutyholder an evidence base for decision-making. If enforcement action ever follows an outbreak, complaint or investigation, one of the first questions will be whether the responsible person understood the system, had assessed the risk, and acted on obvious findings. A current, site-specific assessment supports that position, but only if it reflects the premises as they are now rather than how they looked years ago.

Which Commercial Properties Need A Legionella Risk Assessment

Any commercial premises with a water system that could present a risk should be considered. That includes offices, warehouses, factories, hospitality sites, schools, healthcare premises, gyms, retail units, community buildings and multi-occupied commercial blocks. The trigger is not the size of the building alone. It is whether water is stored, circulated, distributed or used in a way that could allow bacterial growth and exposure.

The commercial property Legionella risk assessment process is essential to ensure the safety and compliance of your building’s water systems.

Further guidance can be found in the legionella control approved code of practice.

In simple terms, if a property has hot and cold water services, outlets that produce fine spray, storage tanks, calorifiers, infrequently used branches, little-used washrooms or complex distribution pipework, there is usually a reason to assess. The same applies where vulnerable people may be present or where there is difficulty maintaining stable control temperatures.

Some dutyholders assume a small shop, office suite or light industrial unit does not need attention because the system looks simple. That can be a mistake. Small systems still develop deadlegs, poor turnover, over-sized storage, tepid cold water and little-used outlets. A straightforward building may require simpler controls than a high-risk site, but it still needs to be reviewed on its own facts.

The dutyholder Legionella responsibilities usually sit with the employer, landlord, managing agent or person in control of the premises, depending on how the building is occupied and managed. In multi-let properties, responsibilities can be shared or split, but that does not make the need for assessment disappear. It simply means the assessor may need to understand where landlord systems end, where tenant control begins, and who holds which records.

Where there is any uncertainty over whether the premises fall within scope, the sensible approach is to assess rather than assume. The risk assessment may conclude the risk is low and the controls straightforward, but that is very different from having no assessment at all.

Regular reviews of the commercial property Legionella risk assessment process can help identify potential hazards before they become significant issues.

What Happens Before The Site Visit

Good assessors do not arrive blind. Before the inspection, they will usually gather background information so the site visit is focused and efficient. This pre-visit stage is where a lot of the quality of the final report is determined.

The assessor may ask for basic information about the property, including the type of premises, how it is used, normal occupancy, known vulnerable users, and whether any parts are vacant or intermittently used. They will often want to know about the water systems in broad terms before attending, such as whether there are cold water storage tanks, booster sets, calorifiers, showers, thermostatic mixing valves, expansion vessels, humidification, process systems or other plant linked to water hygiene risk.

Where records exist, the assessor may review:

• Previous Legionella risk assessments
• Schematic drawings and asset lists
• Temperature monitoring records
• Tank inspection and cleaning records
• Shower cleaning and descaling logs
• Flushing records for little-used outlets
• Sampling results, where sampling forms part of the control regime
• Records of recent remedial works or changes to the water system

This pre-site review helps identify obvious gaps before anyone steps into a plant room. For example, if the previous assessment is several years old and the building has since been refurbished, reconfigured or partly vacated, the assessor already knows the documented picture may not match the live installation. If monitoring records show repeated failures in hot water return temperatures, that becomes an area to verify on site.

There is also a practical planning element. Access arrangements may need to be agreed for roof plant, tenanted areas, locked risers or high-level tank rooms. In larger properties, the assessor may ask for a site contact who understands the building day to day. That person is often more useful than a remote file holder because they can explain which outlets are genuinely used, which areas have become redundant, and what modifications have been carried out informally over time.

Engaging a qualified professional for the commercial property Legionella risk assessment process ensures thorough evaluation and adherence to legal standards.

What The Assessor Looks At During The Inspection

The site inspection is the core of the commercial property legionella risk assessment process. This is where the assessor tests the paper record against the actual building. They will trace the water systems as far as reasonably possible, inspect visible assets, review outlet condition and usage, and look for features that increase the chance of bacterial growth or exposure.

Inspection is not limited to obvious plant. A lot of risk sits in overlooked parts of the system, such as capped pipework after refurbishments, branches feeding removed appliances, low-use guest showers, redundant changing rooms or washbasins in areas that are rarely occupied. The assessor is looking at the whole chain from incoming supply through storage, generation, distribution and use.

Plant And Distribution Systems

The assessor will usually inspect incoming mains arrangements, cold water storage tanks where present, calorifiers, hot water cylinders, plate heat exchangers, expansion vessels, circulation pumps and return loops. They will consider whether design and condition support control of temperature and turnover.

Typical points of attention include insulation, cleanliness, lid condition on tanks, screened overflows, evidence of debris, access for inspection, safe storage temperatures and whether pipework appears correctly identified and sensibly arranged. In hot water systems, they may check whether return temperatures appear capable of achieving control targets and whether heat is reaching sentinel outlets in a reasonable way.

Outlets, Aerosol Sources And Use Patterns

At outlet level, the assessor will review taps, showers, spray taps, hose points and any other devices that can create aerosol. They are not only asking whether an outlet exists, but whether it is used often enough, whether it is clean, whether it is thermostatically blended, and whether poor turnover could leave water sitting within the system.

Usage patterns matter. A washroom serving a busy office floor is very different from a shower room in a unit that has stood empty for six months. The physical outlet may look the same, but the risk profile is not. This is why discussions with site staff are often important during the walk-through.

Condition, Design And Signs Of System Change

The assessor will also look for signs that the system has changed since the last review. Commercial premises are often altered in stages. Kitchens are moved, welfare areas are added, washrooms are stripped out, tenants make local changes, and old branches are left in place because removing them is inconvenient. These piecemeal changes are a common source of hidden deadlegs and poor flow.

Even where the system is fundamentally compliant in concept, wear and age can change the risk picture. Scale build-up, failed insulation, inaccessible valves, poorly labelled services and corroded components can all make monitoring and control less reliable.

How Water Systems, Risk Areas And Control Measures Are Reviewed

A Legionella risk assessment commercial premises review is not just a list of assets. It is an evaluation of how the system behaves and whether the current arrangements are enough to keep risk under control. That means the assessor will consider water temperatures, storage conditions, circulation, outlet use, exposure routes and management controls together rather than as isolated points.

In line with ACOP L8 commercial property expectations and HSG274 Legionella guidance, the assessor will usually review whether the basic conditions for Legionella growth are being minimised. Broadly, that means avoiding stagnant water, controlling temperatures, keeping systems clean where relevant, and managing sources of aerosol.

They will often assess risk areas such as:

• Cold water storage with poor turnover or heat gain
• Hot water systems that fail to achieve or maintain satisfactory temperatures
• Long pipe runs to remote outlets
• Little-used outlets and redundant branches
• Showers and spray-generating equipment
• Thermostatic mixing valve arrangements that create warm blended water close to points of use
• Areas with intermittent occupancy or partial vacancy
• Older plant rooms where modifications have not been fully documented

The review of Legionella control measures usually covers both physical and procedural controls. Physical controls include design, insulation, tank condition, return circulation and removal of deadlegs. Procedural controls include temperature monitoring, outlet flushing, regular inspection, cleaning regimes, record keeping and assignment of responsible persons.

A competent assessor should also make proportionate judgements. Not every issue carries the same weight. A short, unavoidable branch in a well-used system is not the same as a long redundant deadleg serving a removed changing area. A single low-use basin may be manageable through flushing, while a large vacant floor with dozens of outlets may require wider isolation, recommissioning or system alteration.

This is where a water hygiene risk assessment becomes genuinely useful. It should distinguish between conditions that need remedial works, conditions that can be managed through routine controls, and conditions that are of low significance provided the existing regime is maintained.

What The Assessor Will Ask For From The Dutyholder

The quality of the assessment depends heavily on what the dutyholder can provide. Even where records are incomplete, the assessor will want to understand who is responsible for the system and how that responsibility is being discharged in practice.

Most assessors will ask for information in four broad areas: management responsibility, system knowledge, operational records and recent change. They may ask who the appointed responsible person is, who undertakes monitoring, whether contractors are used, and how remedial actions are tracked through to completion.

Typical requests include:

• Details of the responsible person and any deputies
• Current monitoring records for hot and cold water temperatures
• Inspection, cleaning and disinfection records where relevant
• Logs for little-used outlet flushing
• Asset registers or simple system descriptions
• Previous risk assessments and evidence that recommendations were reviewed
• Information on changes to occupancy, tenancy or building layout
• Records of plumbing alterations, refurbishments or decommissioned areas

They may also ask practical questions that do not appear neatly in the logbook. Which showers are hardly ever used? Are there any seasonal occupancy changes? Has a floor been vacant for months? Have complaints been raised about poor hot water delivery? Is anyone bypassing a control because it is awkward to operate? These questions matter because system risk often sits in daily behaviour rather than formal documentation.

Where the dutyholder has good records, the assessment is usually sharper and more efficient. Where records are missing, the assessor can still inspect the system, but the report is likely to highlight management gaps and may recommend a stronger written control scheme. For many sites, that is just as important as identifying a physical defect.

If you need a clearer picture of the legal and management framework, Acorn Safety Services points dutyholders to its Legionella book as a useful starting point alongside the live assessment process.

How The Findings Are Rated And Reported

After the site inspection and record review, the assessor pulls the information together into a structured report. The exact layout varies between providers, but a competent report should explain the property assessed, identify the systems reviewed, describe the key risk factors, record significant findings and set out clear recommendations.

The rating of findings is usually risk-based and priority-based rather than purely cosmetic. In other words, the report should not treat every imperfection as equally serious. A missing tank screen, persistent hot water temperature failure, large redundant pipe branch or unmanaged vacant area may justify a higher priority than minor labelling issues or housekeeping points.

Legionella report recommendations often fall into several categories:

• Immediate actions where there is a material control failure or elevated foreseeable risk
• Remedial works to improve system design or remove stagnant sections
• Management actions such as establishing flushing, monitoring or inspection routines
• Further investigation where parts of the system could not be fully verified
• Review actions after building changes, tenancy changes or significant works

A useful report should be specific enough to act on. “Improve control measures” is too vague to help anyone. “Remove redundant branch serving former cleaners’ sink in rear service riser” or “investigate secondary hot water return temperature loss to third-floor east wing” is far more useful because it tells the dutyholder what the issue is and where it sits.

The report should also separate factual observations from recommendations and, where appropriate, note any limitations. If access was not available to part of the system, the dutyholder needs to know that the assessment was not fully verified in that area. That is not a weakness if stated clearly. It becomes a problem only when missing access is ignored and the report reads as though the whole installation was inspected when it was not.

What Happens After The Assessment

The report is not the end of the process. It is the point at which the dutyholder should decide what action is needed, who will carry it out, and when the work will be reviewed. One of the biggest failures in commercial properties is that a reasonable assessment is commissioned, then filed away without any structured follow-up.

After the assessment, the dutyholder should normally review the recommendations, rank them by urgency and convert them into an action plan. Some items may need immediate engineering input, such as removing deadlegs, improving tank protection, correcting temperatures or isolating unused sections. Others may be management issues, such as creating a flushing regime, updating records or assigning clearer responsibility.

For many buildings, the next steps include:

• Completing remedial works within an agreed timeframe
• Updating the written control scheme
• Starting or improving routine monitoring
• Training site staff or contractors involved in water hygiene tasks
• Reviewing vacancy management arrangements
• Setting a date or trigger for reassessment

Reassessment intervals are not fixed by a universal calendar rule. They depend on the property, the complexity of the systems, changes to use, and whether the existing assessment remains valid. Significant refurbishment, system alteration, tenant churn, changes in occupancy, prolonged shutdown or evidence of control failure can all trigger the need for review sooner than expected.

Where remedial work is extensive, it is sensible to treat the assessment as a live management document. The original findings may need to be updated once deadlegs are removed, outlets are taken out of service, calorifier settings are corrected or vacant areas are recommissioned. The goal is not simply to own a report. It is to maintain a defensible and workable control position.

Common Problems Found In Commercial Premises

Across commercial sites, the same broad issues come up again and again. Some are design problems, some are maintenance failings, and some come from buildings changing use faster than the water systems are reviewed.

Common findings in a commercial water system risk assessment include:

• Redundant pipework left after refurbishment or tenancy change
• Little-used outlets in spare meeting areas, vacant floors or former welfare spaces
• Cold water storage tanks with inadequate insulation, poor condition or low turnover
• Hot water temperatures that do not achieve control levels at sentinel points or on return loops
• Over-sized systems serving much lower occupancy than originally designed
• Poor record keeping despite contractors attending regularly
• Showers that are not cleaned, descaled or flushed properly
• Thermostatic mixing valve arrangements that leave warm water standing too far back in the system
• Inaccessible assets that no one has inspected for years
• Unclear division of responsibility in multi-occupied buildings

One of the most common underlying problems is mismatch between building use and system design. A building may have been fully occupied when installed, then partially vacated, subdivided or repurposed over time. Water systems often remain oversized for the new pattern of use, which encourages stagnation and poor turnover. The risk then sits quietly in the background because nothing appears obviously broken.

Another frequent issue is over-reliance on contractors without enough site-side understanding. Contractors can carry out monitoring and remedial works, but the dutyholder still needs oversight. If no one checks whether recommendations have been completed, whether unusual readings are investigated, or whether the asset list still reflects reality, the management system is weaker than it looks.

For background on the organism itself and why control matters, Acorn Safety Services also provides a clear explanation of Legionella bacteria and how exposure risk develops in man-made water systems.

If you are responsible for offices, industrial units, hospitality premises, schools, healthcare buildings or multi-let commercial property, Acorn Safety Services can carry out a site-specific assessment, identify practical control measures and provide clear reporting for follow-up action. Contact us