Legionella isn’t something most people think about until they absolutely have to. But if you’re responsible for a building, whether it’s an office, a residential complex, a school, or a warehouse, then ignoring it could be a serious mistake.
So, what is Legionella? Why is it something that needs assessing? And more importantly, what exactly is involved in a Legionella risk assessment?
What is Legionella?
Legionella is a type of bacteria that can grow in water systems. If it spreads through water droplets in the air, such as from showers, taps, air conditioning units, or cooling towers, people can breathe it in. That’s how Legionnaires’ disease starts.
It’s a type of pneumonia that can be fatal, especially for people with weakened immune systems. This isn’t a fringe issue. It’s serious, and regulations around it exist for a reason. So, a Legionella risk assessment isn’t just about ticking boxes. It’s about protecting people.
Who Needs to Do a Legionella Risk Assessment?
This is where many people get confused. You don’t need to be a health and safety expert to have this responsibility. If you’re a landlord, employer, building manager, or anyone in control of premises with a water system, it’s on you to make sure a risk assessment is carried out.
Does that mean you have to do it yourself? No. But you do need to ensure it happens.
This includes:
- Workplaces – Offices, warehouses, factories, and retail units
- Residential properties – Especially shared housing or blocks of flats
- Public buildings – Schools, hospitals, leisure centres
- Any building with a water system – Particularly those with tanks, cooling systems, or little-used taps
Basically, if water is stored or circulated, especially warm water, it could be a breeding ground for Legionella.
When Should It Be Done?
A Legionella risk assessment isn’t a once-and-done thing. You’ll need an initial assessment, but regular reviews and updates are just as important.
Here’s when to carry one out:
- Before a building is occupied or opened – Get ahead of the risk
After any major plumbing work or system changes – Systems change, and so do risks
When water systems aren’t used regularly – Stagnant water creates the ideal conditions - Every two years minimum – Or sooner, depending on the findings and system setup
And if something changes, like building use or water system updates, don’t wait two years. Review the assessment sooner.
What’s Actually Involved in the Assessment?
A proper Legionella risk assessment isn’t just someone glancing over your pipes. It’s a detailed process that looks at how your water systems are designed, used, and maintained.
It typically includes:
- Identifying all water sources – Taps, showers, tanks, cooling towers, pipes
- Checking water temperatures – Legionella thrives in warm water (20°C to 45°C)
- Looking for stagnant water – Dead legs (sections of pipework not in use), unused outlets, or rarely used buildings
- Assessing system design – Are there any areas where water could sit still or warm up unnecessarily?
- Evaluating current maintenance – Are cleaning and monitoring tasks being done regularly?
The goal is to spot where Legionella could grow and figure out how to reduce the risk.
What Happens After the Assessment?
Doing the risk assessment is just step one. Acting on it is what really matters. Once the assessment is complete, you’ll get a report that outlines the current level of risk, i.e. low, moderate, or high, as well as recommended actions, which might include temperature checks, system flushing, or removing dead legs. You’ll also receive advice on ongoing controls, such as regular monitoring, cleaning schedules, and staff responsibilities.
You might also be given a written scheme of control. This is a plan that sets out exactly how you’ll keep Legionella risks under control going forward. It’s not always legally required, but it’s a good idea – especially for larger or more complex systems.
Is It Always Complicated?
No. If your setup is straightforward – say, a small office with a basic hot and cold water system – the risks might be low, and the controls fairly simple.
But even simple systems can become high risk if they’re poorly maintained or left unused. That’s why the assessment is so important. It doesn’t overcomplicate things; it tells you what needs to be done and helps you avoid problems down the line.
If you’re unsure where to start, you can arrange for a qualified assessor to carry it out. What matters is that it gets done properly.
Why It’s Worth Paying Attention
There’s a lot of talk about compliance, legal duties, and regulation. But strip that away, and it comes down to something really basic: making sure the water systems in your building aren’t putting anyone at risk. It’s about safety, not paperwork.
And once it’s done, you’re not only protected from the legal side of things, but you also get peace of mind knowing you’ve taken action to prevent a real and avoidable danger.
Keep It Simple, Keep It Safe
Legionella might sound like one of those issues that only big buildings or complex sites need to worry about, but that’s not true. It can affect any water system, big or small, old or new.
Doing a risk assessment doesn’t need to be stressful, but it does need to happen. Once it’s done, and you’ve taken any necessary steps, you’re in a much better position – legally, practically, and morally. So if you’re in charge of a building with water running through it, don’t put it off. Know the risks, assess them properly, and keep things safe.
