A 2nd story living quarters is perched atop of a ground floor office.

There is high certainty based on history and observations that there is a slab leak: assume this is the case for this question. It is desirable to find the water feed into the upstairs (entry point for a bypass).


There is a very similar second office / apartment configuration that has a copper pipe, that comes out of the slab, travels behind an office wall vertically and bridges and provides water to the 2nd floor:

enter image description here
The above photo is for the second office. The pipe in question is all copper. It was verified (by cutting the PVC pipe) that the small PVC pipe is the water-feed for a 'sister' location.


A visual inspection was performed to find the water feed for said apartment: a copper pipe candidate is thought to be the the water-feed.

enter image description here

The goal is to confirm that it is the water feed without cutting the pipe.


What tests can be performed on said candidate copper pipe to confirm that it is the water feed? Tests that are simple, easy, can be performed without elaborate tools (especially avoiding cutting) are appreciated. Thank you

  • Look below for a shut off valve. Turn it. See if you have water flowing upstairs. That said, that copper to CPVC line is a supply side line (it certainly isn't drain or vent at that small a diameter), is the question "is this the supply to upstairs?" – FreeMan Apr 30 at 12:30
  • Also, changed "shall be" to "is". "Shall be" indicates a mandate for a future event, while "is" connotes a current happening. I don't think you're intending that there must be a slab leak at some point in the future, most people would prefer to avoid that... – FreeMan Apr 30 at 12:31
  • Also, very closely related, though not quite a dupe. It is the same picture, though... – FreeMan Apr 30 at 12:54
  • @FreeMan After months of searching the candidate-pipe was found last night: so I probably am biased and badly want this to be the feed. Thanks for the updates. The same picture provided to show the "sister" of the system under consideration. – gatorback Apr 30 at 13:06

with all the water off heat the pipe at one location then turn the water on and see if the heat moves in response to this.

the heat is going to move slowly by conduction with the water off, so it may take a few tries to get a definate answer. you could perhaps measure how fast the hot spot cools, with and without water flow.



The vertical copper pipe at the top of the drywall is the slab pipe. This answer documents the details and thought process that confirmed the hypothesis.


I hope this answer helps a future reader.

Because of time constraints and I believe I had a 90+% chance I had the right pipe. The goal was to minimize any water released when cutting the copper pipe in the ceiling.

From the outside, I wrenched the slab pipe open slightly so that the water in the slab would drain. It drained very quickly, which signaled the pipe is close and increased my confidence. The next step was to cut the copper pipe in the ceiling: creating a water feed input port and slab pipe output-port.


When the copper pipe was cut, a few drops of water dribbled out, which again boosted my confidence I had the right pipe. To confirm that this ceiling copper pipe is the extension from the outside, I temporarily connected a PEX pipe to the hypothesis output-port with a Shark-bite push connector for easy install & removal. The open end of the PEX pipe was positioned outside next to the water valve.

This setup allowed me drive water through the leaky slab pipe and out the new PEX pipe. The water that flowed through the PEX pipe confirmed the hypothesis that said ceiling copper pipe is connected to the outside valve and the upstairs feed point.


enter image description here


enter image description here

  • "I wrenched the slab pipe open slightly" what, exactly, does this mean? I'm envisioning you taking a monkey wrench to a piece of copper pipe and twisting until you've created a leak, but I'm also pretty certain that this isn't what you did... – FreeMan May 4 at 12:16
  • @Freeman. Correct, there was a connector that bridged PVC to Copper, which was wrenched on. It was critical that anything done during the evaluation phase could be "undone" to the extent possible. – gatorback May 4 at 16:34
  • I'd have gone with "screwed" instead of "wrenched", but that's probably just me... – FreeMan May 4 at 16:38
  • Or maybe "loosened". – Jasen May 8 at 1:15

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