How to locate and repair a leaking water pipe in bathroom ?
Procedure would be to work backward from the evidence of leakage to its source. You can isolate if it is indeed a water pipe that is leaking by turning off water lines in the area for a period of time. If it stops, it is not a water pipe leak, but may be a drain leak, a vent leak (coming from around the outside of the vent pipe from above). You can drill a small hole in the wall in the suspect area and use an inspection camera if the pipes are pressurized. You can also drain the water lines and pressurize them with air, which you can push to higher pressures and can then identify the leak by the hissing sound of the escaping air.