A dead leg is any part of your house water supply where water cannot circulate. They are most common in extensions to the plumbing system for future use.
An example of a dead leg would be plumbing installed for a future bar sink in the basement. Over the life of the home, as those pipes sit full of water—not circulating with the rest of the house water supply—there is a risk of bacteria growing inside the pipes. The same can happen with bathrooms that are not used very often.
Circulating loops, especially on the hot water supply side is one way to avoid this stagnation of water in the pipes but honestly there is no real easy answer to the problem. When you consider that a dead leg is considered to be anything more than 2 pipe diameters away from the flow of water, it does not take very much to create a pocket of water where water can stagnate. Contaminated watering holes come to mind.
There are increasing numbers of Legionella cases being attributed to Dead Legs and the number of actual illnesses is likely much higher, with many cases of flu-like symptoms going unreported or un-diagnosed.
Recommendations for how homeowners should deal with dead legs is evolving, but certainly any sections that are intended for future use should be properly isolated from the house system until such time as the installation can be completed.
For further information: Promoting Water Quality and Hygiene
By Charles Buell, Real Estate Inspections in Seattle
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Hello Charles,
Thank you for your informational blog.
I am interested in education and the primary subject is residential water heater safety valve compliance.
Whether the user consumer owns a water heater or rents it makes no difference. the USA plumbing codes all reference the CSA standard Z21.22
The standard becomes rule of law in our local plumbing codes.
The point is the standard insists user consumer (MUST) flip the lever annually. This is a test to determine if the safety asses the required volume of water.
It is suggested the lever be activated for 5 seconds or until clean water emits.
Users/consumers have an option of authorizing a professional. The professional is schooled and has tools and spare parts.
This option is best, and I suggest it be performed by professionals because:
The test could be dangerous if the user consumer is not properly trained in hat to d and what the test indicates.
I imaging the junk piled at or about the water heater and an elderly user climbing up to reach the lever.
Not a pretty sight.
there are several classes of our society who should never try this at home.
But a properly conducted test in accordance with the codes and standards would be beneficial. Last week a water heater exploded in Missouri.
The home is lost. I have many similar explosions to point to.
Not to mention the numbers of T &P valves I removed from schools.
The schools are also worried about Dead Legs.
The T &P is a dead leg. The shank of the safety vale does not flush unless some one flushes it.
It is not widely established as a dead leg, but if you have seen what I have seen, and know that someone will drain the tank and re-fill the tank there is a potential for folks to get sick.
I would love to share my works on T &P safety and hope you could benefit with some of this through your blogging!
Best regards
Ned towel
master plumber retired.
Hey Ned, I was not ignoring your comment—awesome stuff—I just never saw it until now for some reason. I am skeptical as to how much of a problem the TPRV is if the tank is appropriately above 130 degrees F—but all the more reason why they should be flushed by testing every now and then. Thanks for commenting.