Isolating the system
Testing each part of the plumbing in turn shows whether the leak is on the supply line, the hot side, an irrigation line or a fixture. That alone rules out a lot of expensive assumptions.
A water bill that jumped, a damp patch that keeps returning or a meter that turns with every tap closed. An independent plumber can narrow the leak down before anything is opened, so the repair is made in one place rather than several.
There is a check you can do yourself. Turn off every fixture and appliance that uses water, then look at the meter in the box near the curb. If the small flow indicator is still moving, water is going somewhere on your side of the meter.

Detection and repair are two separate things. Ask for them to be quoted separately so you are not paying for a guess.
Testing each part of the plumbing in turn shows whether the leak is on the supply line, the hot side, an irrigation line or a fixture. That alone rules out a lot of expensive assumptions.
Pressure testing, listening equipment and moisture readings narrow the leak to a small area. The aim is one small opening in drywall, tile or concrete rather than exploratory holes.
Ask where the plumber expects to open, why, and what the repair will involve if that is right. If the reading is inconclusive, it should be said instead of cutting hopefully.
What happens next depends on where the water is escaping. A leaking fixture or an accessible line is a straightforward repair. A leak in a line under a concrete slab opens up a wider decision about repairing in place, rerouting the line overhead or replacing a whole run, and each of those has different consequences for your floors.
On larger properties in the towns around McKinney, a long service line between the meter and the house is a common culprit, and the wet ground outside often gives it away before anything shows indoors.
If the leak is under the slab, see slab leak repair and the warning signs to watch for. If the water heater is the source, our repair versus replacement guide covers that choice. When the wet ground is outside and the pressure has dropped everywhere at once, the fault is usually on the buried supply run, which is covered under main water line repair. For a line that has already failed outright, go to burst pipe repair.
How much of the system has to be isolated and tested before the leak can be placed. A dripping valve under a sink is found in minutes; a leak somewhere in a slab takes longer. Ask the provider to quote detection and any repair separately.
Usually the leak can be narrowed to a small area without opening anything, using pressure tests, listening equipment and meter readings. Reaching an under-slab leak still means opening the floor, but only at the point that has been identified.
If water is visibly running or a ceiling is wet, yes, at the meter box by the curb. For a slow hidden leak you can usually leave it on until the plumber is there, but keep an eye on it and turn it off if anything changes.
Call and describe the problem to be connected with an independent plumber.