Phantom Leak

[GReynolds929]

When I shut this valve the pressure tank does not bleed down. When I open the valve after an hour or so I can hear water charging the system

Then the leak is downstream from that valve. It is not related the the well, pump, or cistern.

 

[sarg]

Just another guess ...... but I would shut that valve for awhile and then go and check the multiple toilet tank levels. ( The tank ... not the bowl level )
A flush valve flap that's leaking would be my first suspect. A drop of 150 gallons should be notable.

 

[BlueSkyHigh]

My idle mind is curious, but what is that clamp with the wire attached doing?