I installed a Flume water meter meter($200). It’s strapped next to the meter and the induction is converted to flowrate and wirelessly transmitted back to your phone/computer. You can set automatic alerts for various usage patterns, quotas, and irregular small continuous flows that would indicate a leak. Over a couple years it has been pretty accurate, catching not quite fully turned knobs dripping and hard water valve blockages. The batteries last about a year(Lithium single use AA). Installing one of those and turning off individual toilets / sections of the home and viewing the activity log would be much more efficient than trotting back and forth to check the meter and plot it yourself.
In Austin and the surrounding aquifer community there are many areas with very thin topsoil but very porous limestone underneath so the soil might never appear damp. A large tree can also crack a pipe and absorb water faster than it can reach the surface but that’s usually a drain pipe.
To find a difficult leak there are pressure generators(think injection mold hydraulic presses) that can add more pressure to the line and measure if it drops or not with everything closed as well as how much pressure was needed to cause the leak. The instruments are very expensive and I imagine they’d charge a lot for it. Sadly, UNT Health Science research just surplused an extremely expensive setup for like $50 today since nobody is manning the usual surplus/equipment sharing due to COVID. You’d also have to be familiar with the pressure tolerances to not cause more damage.
It might be possible to find acoustically, but most of the leak detectors I contacted in Austin for a pool didn’t have advanced enough signal processing for all of the road and construction noise coming through the ground and I ended up having to make a hydrophone myself. It’s difficult to find a plumber who knows how to use an oscilloscope. For a pressurized line it’s more complicated because the tap and feed would need to be sealed and that’d increase cost. Standard acoustics are detecting water turbulence and can miss leaks that happen at joints because the joints are also turbulent.
Ultrasonic devices exist and are a non-invasive option for measuring section by section but I’m not familiar with them in a residential setting. That might be your best bet if other options are exhausted. Some info avail at https://www.omega.com/en-us/resources/ultrasonic-flow-meter-water-leak
Old-ish might use CPVC in places that can become brittle, especially at the joints. I had one home flood because the plumber swapped a brittle CPVC toilet shutoff valve but the pipe was improperly supported inside the wall and also brittle. The wiggling when fixing the exterior valve cause the interior joint a few feet higher inside the wall to break. If it’s brittle in one place, it’s probably brittle nearby having been exposed to similar degrading chemistry. The original plaster walls had been covered in drywall due to asbestos concerns, so that new leak wasn’t discovered for months until it finally broke through the plaster on the second floor and ceiling collapsed.
Technically speaking one can find cracks in copper lines through electrical resistance but would need to know the blueprints to tell the difference between a crack and joint and that’s not something most people have access to.
A few years ago the city added pressure limiting valves. These can get hard water buildup that keeps the valve slightly open but can be cleaned with CLR. The same can happen with the toilet fill valve inner workings when city work elsewhere leaves metal burrs traveling up the line that wedge in the fill valve and act as a seed for lime buildup. When those are slightly open at all times they can resonate and shake other connections loose. Slowly turning on a bath and listening/feeling for a hum or whistle can indicate this. This type of leak can also be sneaky where the combination of resonance and leaking shakes the toilet tank support bolts loose and the increased tank water weight presses past those gaskets to drain down the backside of the toilet and into the floor - only intermittently and before the toilet automatically flushes itself.
Other people have already added good suggestions - that’s all I know Austin-specific that wasn’t covered.
