When metal piping is the minority in the plumbing, it is not required to be bonded. This does not prevent it from not being bonded if there is a likelyhood of it becoming energized. Take the metal framing mentioned in Florida. The metal framing supports the electrical and plumbing systems. Since there is the likelyhood of becoming energized, i.e. lightening strikes, it stands to reason to ground and bond it. I am not too concern that they will become energized from the house distribution because if wired properly, the OCPD will open. I am more concern with other or "outside sources" that may not be grounded. This will create a potential since the electrical and metal plumbing is grounded to earth.
Odds are the there is not a reason to bond a "isolated" section of pipe. This does not prevent us though not to examine it for the possibility of bonding.
Tap water is not considered to be conductive. Pure water is non conductive. It is the impurities in the water that conducts the current.
Let's say that you are compelled to ground your isolated piece of pipe in your example and the rest of the plumbing to include the main water supply line is made of plastic, you would have to run a ground wire all the way back to the panel.
