Pulled out an old tub, and back in the wall, I found 7 water lines that come up, connect to each other, and then go back down. They were not attached to the tub at all. Why 7??

Can I use these for a new tub faucet location?

enter image description here

  • Can you gain acces to this area from below...? Commented Jul 25, 2021 at 21:41
  • It would help if you'd tell us more about your home style and layout, along with the general plumbing situation.
    – isherwood
    Commented Jul 25, 2021 at 22:19
  • @ThreePhaseEel - not without a lot of digging :) Commented Jul 26, 2021 at 0:50
  • @isherwood - It's a pretty basic 1 story house on a concrete slab in north east USA Commented Jul 26, 2021 at 0:50
  • 3
    It looks like there are two supply-return loops (hot + cold) with 3 branches that service some other things.
    – r13
    Commented Jul 26, 2021 at 0:57

4 Answers 4


Sweated joints in copper tubing are not rated for soil contact. In contact with wet soil a sweated joint can corrode by electrolysis. In original construction copper runs under a slab are continuous lengths of soft copper--no joints of any kind.

When repairs have to be made to copper in soil contact AFIK the only approved joint is the copper-to-copper crimp connection, e.g., ProPress.

One home builder in Austin TX (Matt Risinger) plumbed his whole house in copper with ProPress connections.


The above answer explains that if you are going to have a joint, then the joint must be in the air.

The next question is why there is a joint here at all? The answer is that part of the flow through the larger pipes is being diverted to smaller pipes, presumably to delivery points. Probably one of the larger pipes is carrying cold water and the other hot.

There should be no problem in tapping these loops. You would have to decide whether it was better for your use to tap into the larger line or the smaller one.


You pulled out a tub near these pipes, right? There were hot and cold lines to the faucet for that tub, right? There is a possibility that the two lines to the old tub are originating at these loops. The 1/2" hot line on the right loop may go the hot for the old tub, and one of the 1/2" lines in the left loop may go to the cold for the old tub.

If so, the easiest way to proceed might be to extend the original lines in a wall to the location of the new tub. Or cut off the no longer needed lines at the loop and redirect to the new location.

  • 7
    Ah ok, I guess this makes sense. So it could be sort of a "manifold" where the main water lines are branched out, and it's above ground to avoid corrosion? This seems plausible, so I'll accept this answer! Commented Jul 26, 2021 at 0:51
  • 2
    I may be missing something here, but I don't really see how this answers the question.. it's not known whether or not the sweated joints are in contact with soil or not, and the question was whether or not a tub faucet could be connected here.
    – cutrightjm
    Commented Jul 26, 2021 at 18:53
  • @cutrightjm it answers the first question of "why 7?" by telling me they are normal supply lines, which kind of answers the 2nd question I had. Commented Jul 26, 2021 at 19:54
  • 2
    @Wayne Conrad, the copper tubing used under slabs is soft and is bent into a gentle curve to go from horizontal to vertical to come out of the slab. This tubing comes on long rolls, just like refrigeration grade copper tubing. In new construction there are no joints or fittings of any kind under a slab. Above the slab the copper tubing is hard, unbendable copper connected traditionally by fittings "sweated" tin-copper or other solder. Commented Jul 27, 2021 at 0:44
  • 1
    Probably the right is hot and the left is cold, feeding the sink, shower, and the 3rd cold is for the toilet. There was a bit of artistry involved with the 3/4" feeds spaced perfectly to allow an evenly spaced out-to-in flow of the pipes. You have to respect that. You're going to ruin the feng shui by adding more pipes in some random boorish direction of your choosing. :)
    – jay613
    Commented Jul 27, 2021 at 22:23

From your picture it appears this is on a cement floor, which does not allow access the tubing below without a lot of hassle. I would guess they are Hot and Cold, you can check this by running hot water. I would also guess the right is hot and the left is cold based on the extra water line which probably goes to a comode. Let us know how this works out for you.

  • Ran hot water, and the right side was hot, so that was a good call Commented Jul 26, 2021 at 14:55
  • Thanks for letting me know. In our area we are not allow joints in cement because of the problems. This way they could connect the pipes together and keep the inspector happy. Copper pipe is now about 20 - 21' in the big box stores. They sell a soft copper that I believe is 60'. I do not know the size of your home but I have a feeling there may be more connection locations like that.
    – Gil
    Commented Jul 26, 2021 at 16:21
  • @Gil, from personal experience on the previous house. It was not just the joints that were a problem. Copper itself corrodes in concrete. The plumber had wrapped the pipes before the concrete was poured, standard practice in NZ. Yet, 10 years later, most pipes that were actually touching concrete (as they came out of it) had sprung a leak at that point. Commented Mar 2, 2023 at 14:02

I don't really know, but here are a few guesses...

  • It allows for future valving and other reconfiguration of branch lines
  • It minimizes the number of inaccessible connections in case of leaks
  • It was easier to do the sweat joints where they're more accessible and visible
  • It exposes a sort of map of the layout of the system

Assuming that those aren't actually floor heat loops, you should be able to branch for other uses. Just branch directly from the 3/4" line, even if it means pulling the whole thing off and starting fresh to create more space.


Not qualified to answer the question, though the idea that someone in the past wished to run lines off the below-slab lines broke open the concrete in this convenient place (the white drain/vent line looks like it was there when the concrete slab was poured, but the copper pipe area looks broken open, though another might disagree), brought up the supply lines and tapped off to run to service points. But since those lines look like they are UNDER the slab, it seems this might've been around the time the house was built. One can fairly easily (for... certain values of "fairly" as John Ringo might write), run lines under any concrete, though definitely straight lines, so the under-the-slab line COULD have happened afterward.

An interesting question.

My real point in writing though is this: if you intend to make use of the installation, perhaps for tub and shower to replace the old one, were I you, I'd DEFINITELY do more than the absolute minimum needed to do so. I'd run the extension up enough to tap off for my needs, but to ALSO allow for future use of the supply lines. The small expense and trouble today would be vastly easier than locating the under-the-slab lines at some future point, especially the breaking through the slab part, to create a new above-slab tap-off. Assuming local code and the home conditions allow for above-slab lines to be run (walls, ceilings, etc.) to other desired points in the home.

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