A leak under the foundation does not show up as a puddle at first. A warm patch of flooring over a hot water line, the sound of water running when every fixture is off, or a water bill that climbs for no reason are usually the earliest signs, and by the time water reaches the surface it has often been running for months.
Shut off the water at the main if the leak seems active and the sound or bill change is new, since that stops the damage from spreading while it gets looked at. There is no way to confirm a slab leak by ear alone, so this is not something to wait on once the signs line up.
In Chula Vista, CA, the plumber we connect you with can pinpoint the leak with acoustic or thermal equipment before any concrete gets opened, and lay out the repair options side by side. Call (844) 898-0295.