Juiceman,
You didn't mention if you friend tried placing anything conductive between the energized water and the sink faucet.
I would think that if either the hot or cold supply lines were metallic and the plumbing was bonded, if you stuck your hand or a jumper wire in the water and then touch a metallic faucet, the GFCI device would most likely have tripped if it was functioning properly.
Since this was sort of an experiment, my guess is that if you measured the voltage from the water to that grounded faucet with the test leads of a high impedance voltmeter, it would probably read the approximate available voltage but not trip the GFCI. If you tried reading this voltage with a low impedance meter or solenoid type tester it would probably would trip.
Seems like it might be a pointless risk though, but I would keep the video recorder running anyway.
