An Introduction to Legionella: What It Is and How to Prevent It
Legionella is a naturally occurring bacterium that can become a serious risk if it grows and spreads in man-made water systems. Left unmanaged, it can lead to Legionnaires’ disease, a severe form of pneumonia that can be life-threatening.
While the risk is real, it’s also highly preventable. With the right precautions in place, you can keep your water systems safe, compliant, and fully under control. Here’s what you need to know.
What makes Legionella dangerous?
Legionella bacteria are found in rivers, lakes and soil, but the danger begins when they multiply in building water systems like taps, tanks, showers and pipework. When water droplets containing the bacteria become airborne (such as through a shower) people nearby can breathe them in.
Legionnaires’ disease mostly affects vulnerable people, but anyone can be at risk if the exposure levels are high enough.
Where the risks lie in your water system
The most common conditions that support the growth of Legionella include stagnant water, warm temperatures (between 20°C and 45°C), and scale or biofilm build-up. These risks are often found in:
Low-use outlets like rarely used taps and showers
Thermostatic Mixing Valves (TMVs) that blend hot and cold water
Poorly insulated pipework or oversized tanks
Systems that aren't being regularly monitored or maintained
How to prevent Legionella growth
Legionella prevention starts with understanding your system and putting the right control measures in place. This typically includes:
1. Temperature monitoring
Water should be stored and circulated at temperatures that inhibit bacterial growth. Hot water must be kept above 60°C in storage and reach at least 50°C at outlets. Cold water should stay below 20°C. Regular monitoring helps confirm this is happening.
2. Regular flushing
Taps and showers that aren’t used often should be flushed regularly to keep water moving and prevent stagnation.
3. Shower head cleaning
Shower heads and hoses should be descaled and disinfected at least every quarter. Scale build-up provides nutrients for bacteria like Legionella to grow.
4. Tank inspections
Cold water storage tanks should be inspected and cleaned to prevent contamination. Drinking water tanks must be kept especially clean and fit for purpose.
5. TMV servicing
TMVs should be serviced regularly to make sure they operate safely. Because they blend water to a lower temperature, they can create ideal conditions for bacteria if not maintained properly.
6. Clean and disinfection
If a system has been left unused or has tested outside safe parameters, it should be cleaned and disinfected thoroughly to restore safe conditions.
Why it matters
Legionella control isn’t just a best practice, it’s a legal duty. If you’re a landlord, building owner, facilities manager or duty holder, you’re required to assess and manage the risk in accordance with ACOP L8, HSG274, and the Health & Safety at Work Act 1974.
Failure to do so can result in serious health consequences and legal action, but with professional support, it’s easy to stay ahead.
ClearSafe can help
At ClearSafe, we specialise in water safety. From risk assessments and temperature monitoring to cleaning, disinfection and remedial works, we offer straightforward support that keeps your system safe and compliant.
If you're unsure whether your building is at risk or want to put a proper water hygiene programme in place, speak to our team today.
We like to keep things simple
Getting water safety sorted doesn’t need to be complicated.
Here’s how it works…
1
We assess your site
We review your setup, identify risks and find out what’s needed to meet compliance.
2
We build your plan
We create a clear service plan based on your property and responsibilities.
3
We take care of it
We handle the work, the checks and the reporting so you stay safe and compliant.
Let’s make water safety simpler, together.
Whether you need expert advice, urgent support or a full compliance plan, we’re here to help.