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What are dead legs and dead ends?
In general terms, a dead leg and a dead end are the same: they are sections of pipework that are redundant or very infrequently used. As a result, water will stagnate within the pipe, leading to a build-up of organic matter like sludge and slime that in combination can encourage and release harmful contaminants into the water.

What is the difference between a dead leg and a dead end?
There is one key factor that differentiates the two: whether or not they are connected to another part of the water system.

Dead legs leads to other sections of the water system, for example another pipe, an outlet or a valve. This means that the cause is usually because a particular outlet is no longer being used.

In contrast, a dead end is a pipe that is completely closed off and does not lead to anything else. The water flow stops when it reaches the end and has nowhere else to go.

Are they dangerous?
The presence of dead legs and dead ends are incredibly dangerous. They increase the risk of deadly microbiological bacteria, like legionella, growing within the water system. Since the pipe is not being flushed, the following can occur:

Stagnant water – water that isn’t being flushed will collect in the pipework at a temperature that is suitable for legionella to grow in
Sludge and slime – over time, organic particles leave a residue on the inside of pipes
Corrosion – irregularly used pipework are more likely to suffer corrosion, especially if organic matter and stagnant water is present
All of these factors work together to create a kind of domino effect. The stagnant water leads to a build-up of organic material which then, together with corrosion, gives legionella the nutrients it needs to grow at an increased rate.

How do you stop them?
The best way for prevention is by simply monitoring the water system for usage and carrying out regular flushes. If a particular bathroom, for example, is not currently in use then someone should run the outlets once a day or weekly depending on the level of risk. This will keep water flowing through the pipework and prevent stagnation from taking hold.

To remedy a dead leg or dead end that has already developed in the system, a complete removal of the pipe may be necessary, which will eliminate all potential hazards. An alternative solution for a dead end is to add an additional pipe that will prevent stagnation by allowing water to flow through.

It should be noted that all buildings, and subsequently their water systems, will differ. The only way to know the risks present is by carrying out a legionella risk assessment.

This is a general overview of dead legs and dead ends, and only one of the many factors that can pre-dispose harmful bacteria to develop in your water system. For a more comprehensive understanding of how to identify and treat them, contact one of our water treatment experts, or download our guide below for further understanding of legionella compliance.

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What are Dead Legs?
January 23, 2018
Dead legs may bring a gruesome image to mind, but in the context of water borne pathogens, it has another negative connotation. The term “dead leg” is actually used to describe a potable water piping configuration in a distribution system where water flow has ceased.

Why does this create a potential health problem?

Dead legs are sections of potable water piping systems that have been altered, abandoned or capped such that water cannot flow through them. This includes isolated branch lines, pipe sections with closed valves and pipes with one end capped. Dead legs experience periods of no flow which leads to stagnation. Basically any closed valve not connected to a fixture, appliance or piece of equipment can be considered as a dead leg.


Credit: OSHA

Dead legs may be intentionally installed to facilitate future expansion of a building’s potable water plumbing system in order to avoid a complete building outage. Dead legs can be roughed in to provide options for future construction or anticipated needs. In many cities, underground dead legs were installed to facilitate potable water infrastructure expansion systems. Functional dead legs can result from lack of use, such as when different wings of a hospital or floors of a hotel are closed due to low occupancy.

While dead legs themselves are not directly harmful, they create a stagnant condition, which can in turn support microbial amplification, including Legionella. In these areas of low or no water flow, the residual disinfectant present in the water to inhibit the growth and amplification of Legionella and other waterborne pathogens can be quickly reduced. Once the disinfectant is consumed, and no other water and disinfectant is introduced into the piping due to lack of flow, Legionella and other waterborne pathogens can amplify. Biofilm can accumulate in areas of stagnation, low flow or eddies which can also contribute to a host of other issues.

By design, dead legs are rarely found in modern, single family homes. Commercial buildings, multifamily residential and senior living centers are far more likely to have dead legs. Buildings undergo frequent modernization, remodeling and tenant improvements, which mean potable water plumbing changes can result in dead legs. Hospitals, hotels or other buildings can become offenders since they constantly renovate or expand facilities. Changing use and occupancy or having numerous piping systems connected to equipment and many plumbing fixtures can also be problematic. Those facilities that also serve a population whom are susceptible to contracting Legionnaire’s disease should make every effort to reduce dead legs in their system.

Dead legs are not limited to potable water plumbing systems in buildings. Fire hydrants, by virtue of their installation as standalone devices, could also be considered dead legs. Unless the fire hydrant is in active use, there is no flow through a fire hydrant. Water sitting inside the branch piping to the hydrant is rarely used and can become stagnant. When the water is released from the fire hydrant, it is released with such force that the stagnant water is aerosolized, creating a Legionella exposure scenario.



What should I do?

To reduce the risk of Legionella amplification in dead legs, building owners and risk managers should:

Identify the areas in your water systems where the water may stagnate, like dead legs or in storage tanks that are not frequently used. In areas of low use, periodically open all faucets, shower heads or other fixtures to flush water through the pipes.
Remove dead legs and unused equipment and water lines from the system.
When installing piping for future use, install a valve as close to the main water pipe as possible to cut off water to the potential dead leg. When removing a fixture from an existing plumbing system, such as removing a kitchenette from a closet, turn off the valve at the main water pipe and open the fixtures to remove any standing water prior to capping the pipe.
Identify and test the integrity of all backflow preventers per local code requirements.
Overall, the building potable water system should be routinely evaluated for stagnation. Chlorine or other disinfectants should be administered to prevent Legionella and other waterborne pathogens from amplifying.

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Removing Dead Legs from Hot & Cold Water Pipes to Prevent Legionella
Removing Dead Legs from Hot & Cold Water Pipes
Dead legs may sound like something you get after sitting for too long, but when they are found in water systems they can present a significant risk to people as they encourage the stagnation of water and the growth of potentially dangerous bacteria such as legionella.

The term dead leg, or dead end is typically used to describe a run of pipework that is no longer in use or a pipe that has become isolated from the regular flow of water.

The term can also refer to a run of pipework that is only used very occasionally. In such instances, this lack of use can lead to water stagnation and increase the risk that the water inside the pipe becomes contaminated with potentially dangerous bacteria, including legionella.

This contamination can lead to problems within the rest of the water system and should be avoided.

Learn more about Legionnaires’ disease here
Is removing dead legs from your water pipes a good idea?
If you know a length of pipework forming part of your hot or cold water distribution system is never used, or has become isolated then steps should be taken to remove it entirely, rather than simply capping it off.

Capping it will simply lead to stagnant water collecting inside the pipe.

This in turn leads to a greater chance for bacteria to multiply in that water, including the Legionella bacterium.

DIY legionella test – no prior experience, simple, easy to use with results in 25 minutes
This can in-turn lead to Legionnaires’ disease and Pontiac fever, a less harmful yet still problematic condition stemming from legionella bacterial contamination.

… as a rule of thumb the maximum size of a dead pipe or dead leg should be no longer than 1.5 x its width

As a rule of thumb, and according to guidelines, the maximum size of a dead pipe or dead leg should be no longer than 1.5 x its width.

If you are unsure about removing dead legs safely and to ensure they are done properly, you can hire an expert familiar in dealing with such pipework.

Why you should always start with a legionella risk assessment
What if the water pipe is used only occasionally and cannot therefore be removed?
While this scenario is not ideal, if it cannot be avoided you should consider how you can make the dead leg less dangerous if it needs to be retained within the water system.

The most obvious way to do this is to flush the pipes through periodically.

This makes it harder for any bacteria to remain, and ensures the system is safer than it would otherwise be.

Should you test your water for Legionella bacteria?
Review your legionella risk assessment
If you are the designated responsible person, responsible for the upkeep of a hot or cold water system, you should have a legionella risk assessment and risk management procedures in place.

This report should account for all dead legs in the system.

Those that cannot be removed under the conditions stated above should be regularly reviewed to ensure the proper steps are taken to reduce risk factors.

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638