Sure you can bond a grid to the EGC, that grid is not the water system for the house. Sure you have to bond metallically isolated sections of metal that may become energized. But when you have a complete metal water piping system, bonding a piece of equipment to it at any point other than as allowed in 250.104, I contend it is wrong and also not a good idea. You risk someone getting shocked at any point on the water system if the motor shorts to the casing if it is bonded to the water piping system. Imagine bonding a gutter at the top section, to say a recept installed in the eave, then bonding it again to a recept near grade. If something shorts out on the eave recept, the gutter becomes a ground path and if someone is touching it could get shocked. Same concept for the water piping.
I don't know what you guys see normally, but all I have ever seen is copper or galvanized water piping from the main all the way throughout the building and that is the reference of thinking I am using. I haven't seen any PEX used in this area.
There is nothing wrong with parallel EGC's as long as they are one of the types allowed by 250.118, which copper tubing is not.
