What Is a Legionella Risk Assessment?
If you're responsible for a building's water systems, you've likely heard the term "legionella risk assessment", but what does it actually involve, who is legally required to have one, and how long does it take? This guide covers everything you need to know.
What Is Legionella and Why Does It Matter?
Legionella bacteria is a naturally occurring bacterium found in freshwater environments. In buildings, it can multiply rapidly in water systems where water is stagnant or temperatures sit between 20°C and 45°C. It becomes dangerous when inhaled as fine water droplets (aerosols). Legionella pneumophila is the most well know species known to be able to cause illness and is the most researched historically, however recent research has evidenced that other members of the Legionellaceae family can also cause disease.
Legionnaires' disease is a potentially fatal form of pneumonia caused by breathing in those contaminated aerosols. High-risk sources include cooling towers, hot and cold water systems, spa pools, and air-conditioning units with evaporative cooling.
The Health & Safety Executive's Approved Code of Practice L8 and technical guidance documents HSG274 Parts 1-3 and HSG282 set out the legal framework that building managers must follow to control this risk. Additional guidance is also available for specific environments / industries such as Health Technical Memorandums for Healthcare and a PABIAC document for the Paper Mill industry.
What Is a Legionella Risk Assessment?
A legionella risk assessment is a formal inspection of your water systems carried out by a competent assessor. Its purpose is to identify conditions where Legionella bacteria could grow and spread, putting occupants and visitors at risk.
A thorough assessment covers five key areas:
1. System survey The assessor inspects every water system and asset on site, which could include tanks, pipework, outlets, heating and cooling plants to understand how water flows through the building. Existing schematics will be audited to determine if they are still current or require updating.
2. Risk identification Dead legs (sections of pipe where water doesn't flow), infrequently used outlets, poorly insulated pipes, and any conditions that allow bacteria to thrive are identified and recorded. A full audit of current management controls and records held. This will include competency and training held by the responsible person.
3. Temperature checks Hot water must reach 60°C in storage cylinders and 50°C at outlets within one minute. Cold water must remain below 20°C throughout the system.
4. Population risk The vulnerability of building occupants is considered. Hospitals, care homes, and hotels carry higher risk than a standard office, for example. Susceptibility of the wider population us also considered where assets with the ability to affect the wider population are present.
5. Written report and action plan You receive a detailed written report outlining any risks found and a prioritised list of corrective measures, along with a recommended review date.
Who Needs a Legionella Risk Assessment?
Under the Health and Safety at Work etc. Act 1974 and the Control of Substances Hazardous to Health Regulations 2002 (COSHH), anyone with a duty of care over a water system in a non-domestic setting is legally required to carry out, and document, a legionella risk assessment.
This includes:
- Commercial landlords and property managers
- Hotels, B&Bs, and holiday lets
- Hospitals, care homes, and GP surgeries
- Schools, colleges, and universities
- Industrial and manufacturing sites
- Offices and co-working spaces
- Gyms, spas, and leisure centres
- Houses in Multiple Occupation (HMOs) and residential blocks
Private homeowners are not legally required to have a formal assessment, but are strongly advised to carry out basic checks, especially if the property has been unoccupied for a period, or has a hot tub or water feature.
Failure to comply with your legal duty can result in prosecution, unlimited fines, and in serious cases, imprisonment.
How Long Does a Legionella Risk Assessment Take?
The time required depends on the size and complexity of the building and its water systems. As a general guide:
Small properties (flat, small office, HMO) Typically 1–2 hours on-site.
Medium properties (hotel, school, mid-size commercial building) Typically half a day to 1 day. Multiple water systems and a greater number of outlets extend the survey time.
Large or complex sites (hospital, university, industrial/ manufacturing sites) Can take 1–3 days or more, and may involve a team of assessors working across multiple areas.
Once the on-site visit is complete, the written report is reviewed and sent to you for your records. At Enviroteam Services, we aim to walk you through the findings in the document to ensure you understand the risk of legionella on your sites.
How Often Should a Legionella Risk Assessment Be Reviewed?
The HSE recommends reviewing your existing assessment regularly; as a company we recommend annually. A new assessment should be commissioned if:
- There are changes to the water system or how the building is used
- The results of currents checks suggest the control measures are no longer effective
- A case of Legionnaires' disease is linked to the premises
- The building has been unoccupied for a significant period
Useful Resources and Further Reading
Below are links to the key HSE guidance documents on legionella control:
- HSE Approved Code of Practice L8 — the primary legal framework for controlling legionella in water systems
- HSG274 Parts 1-3 Technical Guidance — detailed technical guidance covering hot and cold water systems, cooling towers, and other risk systems
- HSE Legionella Hub — the HSE's main resource for legionella control guidance and legal duties
Ready to Book Your Assessment?
Enviroteam Services is a certified member of the Legionella Control Association for legionella risk assessments, supporting industrial and commercial clients across the UK. Our experienced assessors will survey your site, provide a detailed written report, and advise on any required control measures.
Get in touch today:
📞 +44 (0) 1698 642 643 ✉️ enquires@enviroteamservices.co.uk 🌐 www.enviroteamservices.co.uk/contact
Frequently Asked Questions
Is a legionella risk assessment a legal requirement? Yes. Under the Health and Safety at Work etc. Act 1974 and COSHH Regulations 2002, duty holders must assess and control all risks within a workplace. This includes legionella bacteria in their water systems. Failure to do so can result in prosecution, unlimited fines, and imprisonment.
Who can carry out a legionella risk assessment? The assessor must be a "competent person", someone with sufficient knowledge, training, and experience of water systems and legionella control. For anything beyond the simplest systems, using an accredited specialist is strongly recommended.
How much does a legionella risk assessment cost? Costs vary depending on site size and complexity. Contact Enviroteam Services for a tailored, no-obligation quote.
What happens after the risk assessment? You'll receive a written report detailing any risks found and a prioritised action plan. Enviroteam Services can also provide ongoing support including working with customers to provide a written scheme of control, monitoring and water treatment services to keep your systems compliant year-round.
Does a legionella risk assessment cover domestic properties? Private landlords renting out residential properties are legally required to assess legionella risk as part of their duty of care. Homeowners living in their own property are not legally obligated, but should be aware of the risk — particularly if the property has been vacant or has a hot tub or water feature.