1) I assume that a 3rd ground wire was run directly from a GFCI receptacle to a nearby cold water pipe? If I am misunderstanding your comment, let me know..... thanks!
If so, that is not code complaint. The green grounding screw on any receptacle or switch is for the equipment grounding conductor or as the National Electrical Code refers to it as the "EGC". For any branch circuit, the EGC originates directly from the main electrical panel and not a cold water pipe. The grounding wire from the city supply, ie, street side of the water meter is reserved for the Grounding Electrode Conductor or the GEC. The GEC is connected or grounded from the water supply pipe back to the electrical panel neutral bus bar. A cold water pipe is considered as a Grounding Electrode and not equipment.
Typically, a supplemental grounding electrode is also run the main electrical panel neutral bus bar to an 8 foot copper ground rod near the meter socket. A receptacle or a GFCI receptacle is considered as equipment, same as the main electrical panel is considered as equipment. Equipment's are bonded together using an Equipment Grounding Conductor via metal conduit or a bare copper EGC inside a Romex cable. EGC's always originate at the main electrical panel and not directly to a cold water pipe. At the panel, the EGC and the GEC are bonded together via the neutral busbar. The only exception to this NEC rule is if an electrical panel is wired as a sub-panel, then the grounding requirements are different.
2) All branch circuits originate at an electrical panel. Since a branch circuit will require a single or multiple hots and/or a neutral conductor and an equipment grounding conductor, all of these conductors are considered part of the branch circuit and cannot be split-up. If bypassing the EGC for the receptacle and not going back to the main panel but to a cold water pipe is considered as splitting up the branch circuit and that is not allowed per the NEC. All branch conductors must originate from their point of origin, ie the main panel. In addition, all branch conductors must reside within their own cable sheath or conduit and cannot be split or broken out from one another.
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