About Legionella
Legionella is a bacteria that can grow in man-made water systems and, if inhaled in tiny water droplets, may cause serious illness. Understanding how Legionella behaves and how risks are controlled is essential for anyone responsible for a property or water system.
At The Testing Lab PLC (TTL), we help dutyholders stay compliant through Legionella risk assessments, water management policies, monitoring programmes, and remedial support.
What is Legionella?
Legionella refers to a group of bacteria found naturally in water. In most natural environments (lakes, rivers, reservoirs), Legionella is present at low levels and rarely causes illness. Problems arise when the bacteria multiply in purpose-built water systems where conditions are favourable.
What is Legionnaires’ disease?
Legionnaires’ disease is a potentially fatal form of pneumonia caused by inhaling water droplets (aerosols) contaminated with Legionella. Less serious Legionella-related illnesses include Pontiac fever.
Symptoms often start like flu (fever, chills, cough, muscle aches) and may progress to pneumonia. Early medical treatment is important.
Where Legionella bacteria are found
Legionella can grow in a wide range of man-made water systems, including:
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Hot and cold water services (tanks, calorifiers, pipework, showers, taps)
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Cooling towers and evaporative condensers
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Spa pools, hot tubs and hydrotherapy baths
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Decorative water features and sprinklers (where aerosols can form)
Any system capable of storing, recirculating or aerosolising water can become a risk if not properly managed.
How people catch Legionnaires’ disease
People usually catch Legionnaires’ disease by inhaling very small droplets of contaminated water suspended in the air. This is why showers, cooling systems, spa pools and similar aerosol-producing equipment can be higher risk. It is not typically spread person-to-person.
Conditions that allow Legionella to grow
HSE guidance highlights three main factors that encourage Legionella growth:
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Water temperature between 20–45°C (the optimum range for multiplication).
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Stagnation / low flow, allowing biofilm to develop.
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Nutrients, such as rust, sludge, scale, organic matter or biofilm.
Risk increases when these conditions coincide in parts of a system.
To discuss Legionella compliance, risk assessments, monitoring programmes or remedial support, contact our dedicated Legionella specialists:
Tel: 0800 177 7264
Email: info@thetestinglab.eu
Or please complete our online request a call back form by clicking the “Call Me” button, and we’ll respond promptly.
How people catch Legionnaires’ disease
People usually catch Legionnaires’ disease by inhaling very small droplets of contaminated water suspended in the air. This is why showers, cooling systems, spa pools and similar aerosol-producing equipment can be higher risk. It is not typically spread person-to-person.
Who is most at risk?
Everyone can be infected, but risk is higher for:
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People over 45
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Smokers and heavy drinkers
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Those with chronic respiratory/kidney disease, diabetes, heart/lung disease
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Anyone with weakened immune systems
Because vulnerable groups are common in workplaces, housing and public buildings, Legionella control needs to be systematic and proactive.
UK legal duties for controlling Legionella
In the UK, Legionella control is primarily governed through:
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The Health and Safety at Work etc. Act 1974
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COSHH Regulations (Control of Substances Hazardous to Health)
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HSE Approved Code of Practice L8 and supporting guidance HSG274
HSE states that employers and those in control of premises (including landlords) must:
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Identify and assess Legionella risks
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Prevent or control those risks
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Implement, manage and monitor control measures
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Keep records
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Appoint a responsible person to manage compliance
A written scheme of control is expected where risks are identified.
How Legionella risk is controlled (overview)
Legionella control is about stopping the bacteria from multiplying and preventing exposure. Typical measures include:
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Keeping hot water hot and cold water cold (temperature control)
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Avoiding stagnation through good system design and regular use/flush regimes
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Cleaning and maintaining tanks, calorifiers, showerheads, cooling equipment
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Treating systems where needed (e.g., biocide dosing for certain plant)
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Regular monitoring and review based on risk assessment
The exact controls depend on your system type, usage, and risk profile — which is why a competent risk assessment is the starting point.
Frequently asked questions about Legionella
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Your analyst, Lee, was very helpful and his suggestions and advice appreciated.
We would have no hesitation in recommending The Testing Lab and will be in touch soon with regards arrangements for a full asbestos survey for the rest of the site.
TTL have been working directly as my analyst for the last 12 months on a very complex asbestos removal scheme, they have achieved all of their KPI’s without fail and on a number of occasions surpassed their SLA in acting for us on planning issues associated with the demolition in regard to contamination which cannot be removed as part of the normal sequence of operation.
There reports are always issued within timescales and they have policed the reports by the Licensed asbestos contractor faultlessly sometimes in very difficult circumstances.
