Do you always need a professional Legionella risk assessor?

No. A professional Legionella risk assessor is not always required for every simple property or small premises.

HSE explains that carrying out a Legionella risk assessment is the responsibility of the employer, landlord or person in control of the premises. You may be competent to carry out the assessment yourself, but if not, you should get help and advice from a competent person. Read the HSE guidance on identifying and assessing Legionella risk.

This means the key question is not simply “do I need a professional?”, but:

Is the system simple enough, and am I competent enough, to assess it properly?

If the answer is yes, a guided assessment may be suitable. If the answer is no, you should use a competent professional.

If you are assessing a simple property or small workplace, you can use our online Legionella risk assessment to create a structured assessment record.

What does “competent person” mean?

A competent person is someone with enough training, knowledge, experience and authority to help manage the risk properly.

For a simple domestic-style hot and cold water system, competence may be fairly straightforward. For a complex building, stored water system, specialist water system or higher-risk premises, competence may require detailed technical knowledge.

HSE says a competent person should have sufficient authority, competence, necessary skills, knowledge of the system and experience. Read the HSE guidance on managing Legionella risk.

When a guided self-assessment may be suitable

A guided Legionella risk assessment may be suitable where the property is simple, low-risk and the person completing it understands the water system.

Examples may include:

• A small rented house or flat with a normal domestic hot and cold water system
• A simple small office
• A small shop or low-risk workplace
• A premises with no cooling towers, spa pools, healthcare use or complex plant
• A property with straightforward pipework and normal hot/cold water outlets
• A system where hot and cold water temperatures can be checked easily
• A property where showers, little-used outlets and tanks can be reviewed clearly

HSE notes that all systems require a risk assessment, but not all systems need elaborate control measures. A simple risk assessment may show the risks are low and being properly managed. Read the HSE guidance on Legionella risks in the workplace.

When you should use a professional Legionella risk assessor

You should use a professional Legionella risk assessor when the water system, building, occupants or level of uncertainty means a simple guided assessment is not enough.

The sections below explain the main situations where professional input is recommended.

1. You do not understand the water system

If you cannot identify the basic water system, you should be cautious.

For a simple assessment, you should normally be able to understand things like:

• How hot water is produced
• Whether there is stored hot water
• Whether there is a cold water storage tank
• Whether showers or spray outlets are present
• Whether there are little-used outlets
• Whether any outlets are difficult to access or inspect

If you cannot tell what type of system you have, whether storage tanks are present, or whether parts of the system are unused or redundant, a professional assessor may be needed.

2. The premises has a complex hot or cold water system

Some systems are more complex than a normal domestic-style hot and cold water setup.

You should consider professional assessment if the property has:

• A large plant room
• A calorifier or large stored hot water system
• A boosted cold water system
• A secondary hot water return or circulation loop
• Multiple tanks or large storage volumes
• Long pipe runs across a large building
• Multiple floors, wings, zones or remote outlets
• Complicated pipework that cannot be easily traced

Larger or more complex systems usually require more judgement, better records and a clearer control scheme.

HSE’s technical guidance HSG274 includes detailed guidance for hot and cold water systems and other higher-risk systems. See HSE HSG274 technical guidance.

3. The premises is healthcare, care or supported living

Healthcare, care and supported living premises can involve more vulnerable people and higher consequences if controls are poor.

Use a professional assessor for premises such as:

• Care homes
• Supported living accommodation
• Healthcare premises
• Dental or clinical premises
• Premises used by people with reduced immunity or health vulnerabilities

In these settings, a simple online self-assessment is unlikely to be enough. The assessment may need to consider vulnerable users, clinical risks, more detailed water system controls, monitoring and record keeping.

4. There are spa pools, hot tubs, swimming pools or hydrotherapy pools

Spa pools, hot tubs, swimming pools and hydrotherapy pools can create aerosols and may present a higher Legionella risk if not properly managed.

These systems are not the same as a simple domestic hot and cold water system. They normally need specialist knowledge, maintenance, testing and control procedures.

If the premises includes any of these systems, you should use a competent professional rather than relying on a simple guided assessment.

5. There are cooling towers or evaporative condensers

Cooling towers and evaporative condensers are specialist systems and are among the most recognised sources of Legionella risk.

HSE lists cooling towers and evaporative condensers among common sources of Legionella risk in man-made water systems. Read HSE guidance on common Legionella risk sources.

If a site has a cooling tower or evaporative condenser, a simple online assessment is not suitable. A competent professional should be appointed.

6. The system stores or recirculates water

Stored or recirculated water can increase Legionella risk if not controlled properly.

Professional input may be needed where there are:

• Large cold water storage tanks
• Calorifiers
• Secondary hot water returns
• Low-use storage tanks
• Oversized storage for the actual level of use
• Parts of the system where water may stagnate

Simple domestic-style systems may be easier to assess, but large storage and recirculation systems usually need more careful review.

7. Water temperatures are outside the expected range

Temperature control is one of the main ways Legionella risk is managed in hot and cold water systems.

You should consider professional advice if:

• Hot water does not reach at least 50°C at outlets within about 1 minute
• Stored hot water is not kept at 60°C or above where applicable
• Cold water remains above 20°C after running
• Temperatures vary significantly between outlets
• Temperature problems keep recurring
• You cannot access or confirm the relevant temperature points

One failed reading does not automatically mean the whole system is unsafe, but it should be recorded and investigated. Repeated or unexplained temperature issues may need competent review.

You can read more in our guide to Legionella temperature checks.

8. There are dead legs, redundant pipework or little-used outlets

Legionella risk increases where water can stagnate.

A professional assessor may be needed if there are:

• Known dead legs
• Redundant pipework
• Long unused pipe runs
• Little-used bathrooms, showers or outlets
• Empty or partly occupied areas
• Unclear pipe routes
• Areas that cannot be safely accessed

For simple cases, flushing or removing redundant pipework may be enough. For complex systems, the layout and control measures should be reviewed by someone competent.

9. The premises has vulnerable users

The people using the premises matter. A system that might be low risk in a simple workplace could be more concerning where vulnerable people are exposed.

Professional advice may be sensible where the premises is used by:

• Elderly people
• People with reduced immunity
• People receiving care or treatment
• Young children
• People who may be more vulnerable to infection

If vulnerable users are present and the water system controls are uncertain, a competent professional assessment is usually the safer route.

10. The building has been vacant or partly unused

Empty, vacant or partly unused premises can create stagnant water conditions.

This can apply to:

• Void rental properties
• Holiday lets between bookings
• Student accommodation outside term time
• Offices or workplaces with reduced occupancy
• Premises closed for refurbishment
• Buildings or areas reopened after long periods of non-use

For a simple property, flushing and checking outlets may be manageable. For larger or more complex premises, professional advice may be needed before normal use resumes.

11. You need a written control scheme or ongoing monitoring programme

If a risk assessment identifies a significant risk, the dutyholder may need a written control scheme and ongoing control measures.

HSE’s review guidance asks whether the assessment identifies significant risk and whether a written control scheme is in place to address those risks. Read HSE guidance on reviewing Legionella controls.

Professional help may be needed where the control scheme includes:

• Routine temperature monitoring
• Tank inspections
• Calorifier checks
• Water sampling
• Cleaning and disinfection
• System schematics
• Contractor management
• Detailed record keeping

12. A third party has requested a professional assessment

Sometimes the need for a professional assessor comes from a third party rather than the water system itself.

This may include:

• A local authority
• An insurer
• A landlord or managing agent
• A buyer or solicitor
• A commercial client
• An enforcing authority
• A contractor or facilities management company

If a third party specifically requires a professional Legionella risk assessment, a guided self-assessment may not meet their requirements, even if the property is simple.

13. You are not confident completing the assessment

This is the simplest rule.

If you are not confident identifying the water system, understanding the risks, checking the controls or deciding what actions are needed, you should use a competent professional.

A guided tool can help structure the process, but it cannot replace competence where the system or risk is outside your knowledge.

What a professional Legionella assessor should check

A professional Legionella risk assessor should be able to review the water system properly and identify what controls are needed.

Depending on the premises, this may include:

• A description of the water system
• Identification of risk areas
• Hot and cold water temperature checks
• Inspection of tanks, outlets and pipework where accessible
• Review of showers and aerosol-producing outlets
• Identification of dead legs or little-used outlets
• Review of control measures
• Recommendations for remedial action
• Advice on monitoring and record keeping
• A clear report suitable for the type of premises

How to choose a professional Legionella risk assessor

If you need a professional assessor, do not choose purely on price.

Ask about:

• Relevant Legionella training
• Experience with similar premises
• Knowledge of HSE L8 and HSG274 guidance
• Professional indemnity insurance
• What the assessment includes
• Whether a site visit is included
• Whether schematics, photographs or sampling are included
• How actions and recommendations will be presented
• How often the assessment should be reviewed

HSE’s review guidance also highlights checking the competence of external contractors or consultants, including experience, qualifications, training and membership of relevant organisations or trade bodies. Read the HSE review checklist guidance.

When an online Legionella assessment may still be useful

Even where a professional assessor is required, a guided assessment can still help you understand what information may be needed.

For simple properties, an online assessment can help you:

• Record the basic property details
• Identify whether the system appears simple or complex
• Record hot and cold water checks
• Note showers, tanks, little-used outlets and pipework concerns
• Create an action plan for simple issues
• Keep a record for review

For complex systems, professional advice should take priority.

If your property has a simple domestic-style hot and cold water system, you can start an online Legionella risk assessment here.

Quick checklist: online assessment or professional assessor?

A guided online assessment may be suitable if:

• The property is simple and low risk
• The water system is domestic-style and easy to understand
• There are no specialist water systems
• There are no cooling towers, spa pools or hot tubs
• The premises is not healthcare, care or supported living
• You can check hot and cold water temperatures
• You can identify showers and little-used outlets
• You are confident recording the findings and actions

Use a professional Legionella assessor if:

• You do not understand the water system
• The building has complex plant or large stored water systems
• There is a calorifier, boosted system or secondary return
• The premises is healthcare, care, supported living or clinical
• There is a spa pool, hot tub, swimming pool or hydrotherapy pool
• There is a cooling tower or evaporative condenser
• There are vulnerable users and controls are uncertain
• Temperature readings are repeatedly outside the expected range
• The premises has been vacant or partly unused for a long time
• A third party specifically requires a professional assessment
• You are not confident completing the assessment yourself

Final advice

A Legionella risk assessment should be proportionate to the risk.

For a simple rented property, small workplace or domestic-style hot and cold water system, a guided assessment may be a practical way to record the key checks and actions.

For complex systems, vulnerable users, specialist water systems or situations outside your knowledge, you should use a competent professional Legionella risk assessor.

The safest approach is to match the assessment to the system. Simple system, simple assessment. Complex system, competent professional support.

Frequently asked questions

Is a professional Legionella risk assessor legally required?

Not always. HSE says you may be competent to carry out the assessment yourself, but if not, you should get help and advice from a competent person. For simple systems, a guided assessment may be suitable. For complex or higher-risk systems, professional assessment is usually the safer option.

Can a landlord do their own Legionella risk assessment?

In many simple domestic rental properties, a landlord may be able to assess the risk themselves if they are competent to do so. However, if the water system is complex, the landlord is unsure, or the property has higher-risk features, they should get competent professional help.

Do small businesses need a professional Legionella assessor?

A small business with a simple hot and cold water system may not need a professional assessor if the responsible person is competent to complete a suitable assessment. If the premises has complex systems, vulnerable users, stored water, spa pools, cooling towers or uncertainty, professional advice should be used.

Is a Legionella certificate the same as a professional assessment?

Not necessarily. A certificate or report is only as good as the assessment behind it. What matters is whether the risk assessment is suitable for the premises and whether the person completing it is competent for the system being assessed.

When is an online Legionella assessment not suitable?

An online assessment is not suitable for specialist or high-risk systems such as cooling towers, spa pools, healthcare premises, care settings, large complex water systems, or situations where the person completing the assessment does not understand the system.

What should I do if I start an online assessment and realise the system is complex?

Stop and get competent professional advice. A guided assessment can help identify that a system may be outside scope, but it should not be used as a substitute for professional assessment where the risk is complex.