• Lisamarie Lamb

Legionella Control: How To Deal With A Dead Leg

If you have had a legionella risk assessment carried out on your building, or you’ve been speaking to a legionella consultant like the experts at Assured Water Hygiene, you may have heard the term ‘dead leg’. It’s a strange phrase, but as well as that, it can cause a lot of problems in terms of your risk of legionella bacteria, so it’s something you need to take seriously. Read on to find out more about what a dead leg is and what you should do about it.


What Is A Dead Leg?

When it comes to your building’s water system, a dead leg is simply a section of pipework that isn’t used anymore or is so rarely used that an expert plumber could remove it without causing any disruption to the rest of your water services. Dead legs tend to come about when modifications have been made to the building and old pipework is abandoned. Contractors will have removed most of the pipework, but if any remain, it is capped off – and this is a dead leg.



Photo by Daniel Fazio on Unsplash


Why Are Dead Legs A Problem?

When you have water passing through pipework on a regular basis, legionella bacteria don’t have a chance to settle, breed, and cause problems – it’s flushed away before anything bad can happen. The problem with dead legs is that they are not flushed, but water can still collect in them. Because they collect stagnant water and they can often corrode because they’re not taken care of, they are the perfect spot for legionella to call home. Unfortunately, because these dead legs are still often connected to the overall water system, that bacteria can leach into it, and that’s where the big problems start.


How Do You Know You Have A Dead Leg?

If you’re unsure whether you have dead legs in your building, your legionella risk assessment will point them out. Plus, you may be able to spot them on schematics; if you know that there used to be a bathroom or pipework somewhere and then things were changed around, it’s worth checking that area out just in case dead legs remain.


Unfortunately, unless you take the time to investigate your building thoroughly or have an in-depth legionella risk assessment carried out by a professional, you may not become aware of any dead legs until a legionella outbreak occurs. At this point, the building will need to be checked for problems.


What To Do About Dead Legs?

Ideally, you should remove a dead leg entirely. This may be disruptive work – walls may even have to be removed – but it’s the best way to limit the risk. If you can’t remove the dead leg entirely, it should be cut back to be as small as possible – the less pipework, the less water, and the less chance of legionella growing within it. The Water Regulations Advisory Scheme (WRAS) recommends that a dead leg must be no longer than twice the width of your pipe, so a 15mm pipe should have a dead leg no longer than 30mm (although the best option is still to remove it altogether).


If the dead leg cannot be removed or cut back, additional testing for legionella will be required to ensure there isn’t a problem.


Contact Assured Water Hygiene

Assured Water Hygiene has been carrying out risk assessments and examining dead legs for many years, and we are experts in our field. If you have any questions or you need to book a survey, please don’t hesitate to get in touch.

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