The water supply was electrically isolated from the municipal water supply (QEST plastic was replaced after discovery, per code), but there is a direct electrical connection to the neighborhood through metal natural gas lines.
Thank you for answering my first question.
Because your response includes the comment about the metal natural gas (utility ???) lines, I re-ask about your electric supply, with slight rewording, how many neighbors are supplied from the same electric utility transformer that your home's electrical service is connected to.
And, as a second question, I ask if you have investigated the physical characteristics of the natural gas piping and routing? FYI, in my limited experience and knowledge, di-electric union(s) are used at the customer gas meter connection to the supply piping, the effect of which is to electrically isolate the underground pipe from the premises gas piping system. Maybe your local utility has a different policy?
The thrust of my questions is towards an approximate circuit diagram, including probable resistances, of the multiple parallel current paths back to the source (the electric utility transformer grounded service conductor terminal) and the Main Bonding Jumper (as defined in Article 100 of the National Electric Code - NEC).
And, as a third question: What year was the permit issued for the construction of your home? This will fine tune some of our answers, by knowing the version of the NEC likely in effect during construction.