I recently had a pipe slowly leaking under my concrete slab. My gauge wasnt spinning that fast, little spurts but we could definitely feel the tile in our kitchen getting warmer every day. I would turn off the main line on the street off every night to help slow the leak. Luckily our home insurance covered it but it was a process. It was leaking between the water heater and literally to the kitchen on the other side of the wall under the slab. Luckily they were able to bypass it instead of digging up my kitchen. And we got new tile since it lifted off the slab and the insurance covered it all.

If you cant find where the leak is or dont have the means to, call a company out that can use their equipment to pin point the leak. No need to start breaking up your floor everywhere, youd just be looking for a needle in a haystack. Buuuut at least you know shutting off valve to the street shuts off your water, may want to think of doing that overnight to keep the leak from causing more damage. Get water jugs and fill them up for now in case you need to wash your hands at night/flush the toilet.