Your Questions Answered
What Is Legionella & Why Does It Matter?
Legionella is a bacterium found in water systems that can cause a potentially fatal form of pneumonia. Understanding the risks — and your legal obligations — is essential for any property owner, landlord or business in the UK.
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~500 Cases reported in England & Wales annually |
10% Case fatality rate — 1 in 10 die |
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20–45°C Temperature range where bacteria thrives |
£10k+ Potential fine for non-compliant landlords |
What Is Legionella?
Legionella is a family of bacteria (Legionella pneumophila being the most common species) that occurs naturally in freshwater environments such as rivers and lakes. In low concentrations outdoors it poses little risk — the danger arises when it colonises man-made water systems and is inhaled as fine water droplets or aerosol mist.
When inhaled, Legionella can cause two distinct conditions. Legionnaires’ disease is the serious, potentially fatal form — a severe pneumonia requiring hospital treatment. Pontiac fever is a milder flu-like illness that typically resolves without treatment within a few days.
Legionnaires’ disease cannot be passed from person to person. Every case is contracted directly from a contaminated water source — which is precisely why controlling those sources through proper risk assessment is so important.
Where Does It Grow?
Legionella multiplies rapidly in water held between 20°C and 45°C. It thrives where water stagnates, where limescale or sediment has built up, and where biofilm forms on pipe surfaces. Bacteria is killed above 60°C and dormant below 20°C.
How Is It Inhaled?
Infection occurs through breathing in contaminated water droplets — from showers, taps, spa pools, cooling towers and any system that generates fine mist. You cannot catch it from drinking contaminated water.
Which Water Systems Are High Risk?
Any system that stores, heats or circulates water can harbour Legionella — but some present a significantly higher risk.
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Showers & Spray Taps The fine mist from showers is the most common route of infection. Infrequently used showers are particularly high risk. |
Hot Water Cylinders & Calorifiers Water stored below 60°C provides ideal conditions for Legionella to multiply. Older unvented cylinders are a common concern. |
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Cooling Towers & Evaporative Condensers The most serious commercial risk. These systems release large quantities of aerosol and have caused major outbreaks. |
Dead Legs & Unused Outlets Sections of pipework with no flow allow water to stagnate. Common in refurbished or extended properties. |
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Spa Pools & Hot Tubs Warm, aerated water is a well-documented Legionella risk. Regular disinfection and monitoring are essential. |
Cold Water Storage Tanks Older open-top cisterns in loft spaces can warm above 20°C and accumulate sediment, encouraging bacterial growth. |
Who Is Most at Risk?
Most healthy adults will not develop serious illness. However, certain groups face a significantly higher risk of severe disease:
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Over 45s Risk increases significantly with age. The majority of cases occur in people aged 45 and over. |
Respiratory Conditions People with COPD, chronic lung disease or a history of smoking are at heightened risk. |
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Immunocompromised Individuals People undergoing chemotherapy, taking immunosuppressants, living with HIV or managing diabetes are particularly vulnerable. |
Hospital & Care Home Residents Healthcare settings combine vulnerable people with complex water systems — Legionella control is especially tightly regulated here. |
What Does the Law Require?
The duty falls on the person in control of premises — whether a business, landlord, managing agent or local authority.
Health & Safety at Work Act 1974
Places a general duty on employers and those in control of premises to ensure, so far as is reasonably practicable, the health and safety of employees, visitors, tenants and the public.
COSHH Regulations 2002
Covers biological agents including Legionella. Requires employers to assess the risk, implement controls and keep records. Legionella is specifically listed as a hazardous substance requiring formal risk management.
HSE Approved Code of Practice L8
Sets out in specific detail what duty holders must do. Compliance with L8 provides a legal defence; failure to follow it can be used as evidence of negligence in court.
HSE Technical Guidance HSG274
Provides technical guidance for specific system types — evaporative cooling (Part 1), hot and cold water systems (Part 2), and other risk systems (Part 3).
What About Residential Landlords?
Residential landlords are duty holders under health and safety law. HSG274 Part 2 makes clear that landlords must assess and control the risk from Legionella in their properties — whether they own a single flat or a large portfolio.
While a Legionella risk assessment is not a statutory certificate like a Gas Safety Certificate, failing to carry one out can expose landlords to prosecution, civil liability and difficulty with insurers. Local councils increasingly expect to see evidence of compliance.
What Does a Risk Assessment Actually Involve?
A competent assessor will carry out a structured inspection of your water systems, producing a written report documenting findings and recommending any remedial actions.
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1. System Survey & Schematic A full walk-through mapping pipework, storage tanks, outlets, TMVs, showers and dead legs. Photos taken throughout. |
2. Temperature Testing Hot and cold water temperatures recorded at sentinel outlets and storage. Results compared against L8 target values. |
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3. Risk Scoring & Assessment Each identified risk scored based on likelihood and severity, producing a prioritised risk register. |
4. Written Report & Action Plan Clear written report with photos, temperature readings and a plain-English action plan with remedial recommendations. |
How Often Do I Need a Risk Assessment?
The HSE requires the assessment to be kept current and reviewed whenever it may no longer be valid. In practice:
✓ Residential: every 2 years is widely accepted as good practice, plus after any significant system or use changes.
✓ Commercial: annual review typically recommended, with more frequent monitoring in between.
✓ After building changes: any refurbishment, extension or change of use may affect risk levels and warrant a fresh assessment.
✓ After low occupancy: properties unoccupied for an extended period need attention before tenants return.
Frequently Asked Questions
Do I legally have to get a Legionella risk assessment as a landlord?
Yes — landlords are duty holders under the Health & Safety at Work Act 1974 and COSHH Regulations 2002. You are legally required to assess and manage the risk from Legionella in your properties. A written risk assessment from a competent assessor is the standard way to demonstrate compliance. Failure to do so can result in prosecution and civil liability.
Can I carry out my own Legionella risk assessment?
In theory, a person with sufficient knowledge can assess a simple low-risk system such as a standard domestic property with a combi boiler. For anything more complex, or where you want documented evidence of compliance, using a qualified independent assessor is strongly advisable.
What is the difference between Legionella testing and a risk assessment?
A risk assessment is a systematic inspection of your water systems to identify and manage risk — this is the primary legal requirement. Legionella water sampling (laboratory testing for bacteria) is a separate process that may be recommended where elevated risk is identified, but it is not a substitute for a risk assessment.
My rental property has a combi boiler — does it still need a risk assessment?
Combination boilers eliminate the hot water storage cylinder — one of the key Legionella risk factors. However, risk can still be present from cold water systems, showers, infrequently used outlets or supplementary storage. A risk assessment confirms the level of risk and provides the compliance documentation you need as a landlord.
How long does a Legionella risk assessment take?
For a standard residential property, the on-site inspection typically takes 30 minutes to 1.5 hours depending on size and complexity. Commercial premises take longer. The written report is usually issued within a few days of the visit.
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