A slab leak does not show as a puddle. It shows as a warm spot on the floor, the sound of running water with every fixture closed, an unexplained jump in the water bill, or a section of flooring that has lifted for no visible reason.
Detection uses acoustic equipment and pressure testing to locate the leak before anything is opened, because breaking slab to look is expensive and destructive. Locating first is what keeps the repair proportionate.
Repair options are a spot repair through the slab, or rerouting the affected line overhead and abandoning the section in the concrete. Which makes sense depends on the pipe's condition and how many leaks it has already had.
Technician insight
A warm patch on a slab floor is a hot line leaking underneath it. That is not subtle once you know to feel for it, and it narrows the search immediately.