Dead leg pipes or piping are sections of a water system that are either infrequently used or have been made redundant due to building modifications.
As water cannot flow through this pipework, it becomes trapped. In these conditions, sludge and slime starts to build up inside the pipe, causing corrosion and the growth of harmful bacteria like Legionella.
Dead leg piping can occur in both hot and cold water systems, leading to the growth of Legionella if the water cannot be flushed regularly.
To prevent any hygiene risks, we’d recommend removing any unused pipes from the system; however you can also curb this risk through temperature control.
With this particular strain of bacteria it remains dormant in temperatures below 20°C and it cannot survive in environments above 60°C. To therefore prevent Legionella growth in dead leg pipes, for hot water systems we’d recommend keeping water at 50°C or above, whereas for cold water systems the supply should be kept below the 20°C threshold.
Once you have identified dead legs in your pipework and any other areas where water could stagnate, there are a number of modifications that can be made to improve the hygiene of you water system.
The first would be to remove the dead legs and any unused equipment. For any areas where complete removal is not an option, we’d suggest shortening the dead leg pipe as much as possible. To ensure your water is safe from stagnation, the WRAS (Water Regulations Advisory Scheme) recommends that a dead leg should be no longer than twice the width of the pipe.
For the remaining pipework, you can modify this to avoid the creation of harmful dead legs in the future. One example of this would be to install a valve as close to the main water pipe as possible so you can cut off the water supply to a potential dead leg.
Even with these modifications, a building’s water system should continue to be regularly checked for any areas of stagnation.
As water cannot pass through dead leg piping, it remains at a standstill. Left to sit in the pipe, the water will become stagnant which can lead to the growth of waterborne bacteria like Legionella. If the dead leg pipe is then put back into use, this can then cause contamination issues for your whole water supply.
To completely avoid this, we recommend removing sections of dead leg piping where possible as they can pose a serious risk to your water’s hygiene. If it is not possible to remove the dead leg pipes as they still see occasional use, we’d suggest shortening the pipe or adding flushing points so the water can still flow, preventing stagnation.
The main difference between a dead leg and dead end pipe is whether or not they are connected to another part of the water system.
A dead leg section of pipework is still connected to the water system but it has been isolated so that nothing will flow through. Although it is still connected to pipe or valve, this particular outlet is no longer in use.
With dead end pipes, one end is closed off so that is not possible for water to pass through at any point. This normally occurs when there has been a need to change the current water system.