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