Im putting in a new sink in my bathroom, and in doing that Im moving the sink from one side of the bathroom to the other. Ive got the pipes on the new side all ready for the new sink. Im also putting a cap on the end of the old sink pipes. Its just occurred to me that if I just cap the ends just under the floorboards where the old sink used to be, that there will be a metre or two of pipes that have water in, but going nowhere. Does this matter? Is it possible for the water to become stagnant perhaps, or to affect the water supply in any way? Should I try to cap the pipe as close to the T junction (further away under other floorboards) or does it not matter at all? It would save me some time not to pull up other floorboards, but I thought I should ask before I leave a few metres of both hot and cold pipes 'live' but going nowhere. Thanks for any help on this.

1 Answer 1


It is a very bad idea to have a dead leg in a water supply system. These are unswept by flow and so can grow bacteria. Check with your local residential plumbing code enforcement on how serious a violation it is.

  • Thanks Jim. I've ended up with very little, an inch on one and maybe 2 on the other. is that ok or also bad?
    – Luke Smith
    Feb 4, 2017 at 20:23
  • 1
    I honestly don't know, but that sounds short enough so that chlorine from the water in the flow could diffuse into it. It would still be un-swept though. When you get ready to sell the place it could come back to haunt you. Better check with code enforcement; maybe they will say it is not a problem. Feb 4, 2017 at 22:29

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