Today a plumber removed a sink from my house and sealed the two corresponding pipes at the location where they branch from the rest of the system. I expressly asked him to do this because I wanted to avoid having a dead run of pipe in my walls where bacteria could develop and cause serious health risks.

This is the end result. I marked in red where the dead leg starts for each of the pipes that got cut.


I've been reading online about the risk of bacteria such as legionella developing in the system and the recommendation seems to be that the dead leg's maximum length should be at most 1.5 times the diameter of the pipe itself. The dead legs shown in the picture are about 4 times the diameter.

I would like to understand whether this poses a health risk and whether I ought to ask the plumber to come and shorten the pipes.

  • 2
    Are you on a city water supply or well water? If in city water I would not be concerned at all. If on well water I would be worried about other things well before legionella, prior to 1976 this had not been discovered, how often do you actually hear about it? I am sure there will be some that say this is horrible, what about snow birds that don’t use any water for months at a time you don’t hear about them getting sick regularly. I see this as an opinion based question.
    – Ed Beal
    Mar 30, 2021 at 17:47
  • Thanks. I am indeed on a city water supply. Are there additives in the water that prevent growth?
    – kettlepot
    Mar 30, 2021 at 22:27
  • 2
    The water is treated and has a residual chlorine content that kills bacteria. I would not be concerned in the slightest.
    – Ed Beal
    Mar 31, 2021 at 13:48

1 Answer 1


I would not be overly concerned about this unless it was the highest point in your plumbing or if you had low water pressure from the water supply (or if you are on well water).

These couple of inches extra should be flushed with water at all times and recycled with the rest of the water supply. There is no reason to believe that the water in these small sections would remain stagnant, as they are just way too small to have "standing" water.

If you are concerned I would have the plumber not cap these at all, take out the nearest T and change it for a right angle.

Now there are a TON of benefits to block framing (from the materials I am guessing France or Italy) but plumbing and rerouting the plumbing... no. We simply don't have many instances in the US like this because the plumbing is easily modified inside 2x construction.

  • Close, Netherlands :) but this is at a pretty high point in the plumbing. In the photo the pipes go into the ceiling and then route through the house. Does that create an extra concern?
    – kettlepot
    Mar 30, 2021 at 22:28
  • Pretty high point or near/at the highest point? Or level with highest point?
    – DMoore
    Mar 31, 2021 at 3:53
  • I'd say about 20 cm (7.8 inches) away from the highest point (I can't see how far the pipes go into the ceiling before they level off, but I assume not that far).
    – kettlepot
    Mar 31, 2021 at 7:23
  • If it isn't on the highest end and you have a city water source that is pressurized you don't have an issue. If you are that worried about it just have those two Ts replaced. It is not easy taking off a wet T though and your plumber may have issues - so you are introducing two possible points of leaking in the future.
    – DMoore
    Mar 31, 2021 at 18:53

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