While inspecting unit remodel in a multiple occupancy bldg I checked the bonding for the water piping system in the units panel. Traced the bond to the water heater of the unit. 250.104(A)(2) says in essence that if the system is isolated from all other occupancies by use of nonmetallic water piping then the above bonding is acceptable. The question arises: How do you know if there is nonmetallic isolation? You don't The building is old as the hills and who knows if the metal piping system has any isolated areas. So the real question is: If it is left bonded in the unit and there isn't any nonmeatlic isolation will it make a difference anyway? I hate to see the EC have to run a bond in an old building to the service.

Is this a bonding conductor required by 250.104 or a grounding electrode conductor for the service?
Don

It's the bonding conductor per 250.104 for the water piping.

The older the building, the less likely there are isolated sections of pipe.