Refrigerator Sparks when it touches the water line
DO NOT USE THAT RECEPTACLE UNTIL IT IS EXAMINED CLOSELY BY QUALIFIED PERSONNEL

What you likely have with that poor, maligned GFCI is a situation called a "reverse polarity bootleg ground", where neutral and ground are both connected to the incoming hot and  hot is connected to the incoming neutral.  This situation is extremely dangerous, even on a GFCI protected circuit, as the miswired ground puts the chassis of whatever's plugged into it at 120V in a way that cannot be disconnected by the GFCI receptacle.

What you can do to test for this is use a non-contact voltage detector -- place its business end next to the receptacle but not in the slots.  If the receptacle ground is live -- this means that the entire receptacle mounting yoke is hot at 120VAC and will set off the voltage detector.  On a normal receptacle, this won't happen -- the only way to get the detector to go off is to stick the tip in the hot slot on the receptacle.

If that's the case, then you'll need to have the bootlegged "ground" removed (it may be upstream of the receptacle and quite hard to find) and the receptacle polarity corrected as well.  If the receptacle comes up clean, then I'd use the non-contact voltage detector to check the copper water pipe -- if that's hot, then there's a bonding problem and an equipment fault, which is a combination you'll want a qualified electrician to fix.  (Not the least because trying to fix that DIY puts you at even more risk of the 60 cycle shuffle than you're already at!)