[Baz]

Most of the domestic water service lines I have seen first go to the house where there's an isolation valve (cutoff valve to shut the water off to the house, instead of at the meter).

Usually this is at one side of the house, sticking up above the ground maybe 12" or so, and visible.

From there there could be additional water lines running under your slab but I think they usually run through the framing.

Are you absolutely sure the leak is beneath your slab?

Might be worth getting someone else to look at it to verify.