What Is Legionella — and Why You Must Control It

Legionella bacteria can cause serious, sometimes fatal illness. UK law requires property owners and managers to assess and control the risks in their water systems.

Understanding Legionella

Legionella bacteria thrive in water systems between 20°C and 45°C, particularly where water is stagnant or nutrients are present.

Common sources include:

Hot and cold water systems
Showers and spray taps
Cooling towers and evaporative condensers
Spa pools and decorative fountains

When contaminated droplets become airborne and inhaled, they can cause Legionnaires’ disease, a severe form of pneumonia.

A large room filled with lots of boilers and pipes.

Your Legal Responsibilities

If you manage a building with water systems, you have a legal duty to prevent Legionella growth under:

Health & Safety at Work Act 1974
Control of Substances Hazardous to Health (COSHH)
HSE ACoP L8 and HSG274 Part 2

You must:

Conduct a Legionella Risk Assessment
Implement a written scheme of control
Nominate a Responsible Person
Maintain accurate monitoring and maintenance records

Failure to comply can lead to prosecution, fines, or imprisonment.

Legionella Facts You Might Not Know

Contaminated water systems pose a serious risk to life

You are at risk of prosecution if in breach of regulations

Legionella infections have up to a 30% mortality rate

Water Vapour Droplets is the most common way Legionella is contracted

HSG 274 Part 2 and ACOP L8 must be adhered to in all commercial buildings

Persons of responsibility must ensure the water systems are monitored

How to Prevent Legionella

To keep systems safe:

Keep cold water below 20°C and hot water above 50°C.
Flush infrequently used outlets weekly.
Clean and disinfect tanks and calorifiers regularly.
Ensure all changes to systems are risk assessed.
Maintain detailed, accurate compliance records.

Common Mistakes

Common mistakes such as irregular temperature checks, neglected outlets, poor documentation, and untrained staff can quickly turn a low-risk system into a serious hazard. Consistent monitoring, informed management, and proper system design are essential to keeping Legionella under control.

Infrequent temperature testing or poor documentation
Ignoring little-used outlets or redundant pipework
Treating flushing as a substitute for system design
Lack of staff training and awareness

There is another way!

Monitoring Options

Traditional monitoring relies on monthly manual checks often incomplete or inaccurate.

Modern systems like Legionella Watch provide:

Continuous IoT temperature tracking
Instant alerts for temperature anomalies
Digital audit trails for full compliance transparency

Legionella Watch

Frequently Asked Questions

How often should a Legionella Risk Assessment be done?

Every two years or whenever there is a change in your water system or building use.

Is a Legionella Risk Assessment a legal requirement?

Yes — under the Health & Safety at Work Act and ACoP L8, all duty holders must manage the risk of Legionella.

Who can carry out a Legionella Risk Assessment?

Only a competent person with appropriate training and experience, like the trained assessors at LCS.

What happens if my system fails a Legionella test?

We provide clear, step-by-step guidance for remedial actions and ongoing monitoring to restore compliance.

Trusted by leading organisations across the UK.

A row of logos on a white background including joseph , wavertree house , and laurel home surgery.

What You Can Expect

Richard Thornett - Lead Engineer - BSW Southampton

“It is like having an engineer 24/7 with their hand on the plant”

James Shaw - Director - Miller Freeman - Nottingham

"The real time data allowed us to make several minor adjustments and changes to achieve satisfactory temperatures throughout the property that would not normally be picked up."