I am living in a 1964 mobile home and replacing plumbing from city line up. I cut the galvanized going into trailer and got sparks placed meter between two lines and read 20 volts give or take a couple .had replaced under trailer outlet for heat tape but that breaker was off. i ran a jumper from galvanized to city copper for time being .followed ground from breaker box to plumbing to under trailer attached at cross member [rusty cross member ]. Any ideas would be greatly appreciated it is getting cold and i need water badly. Bob
Presumably the metal plumbing was your ONLY ground connection (from both the behavior and your description of the ground wire run.) You might want to have an electrician take a look at the system. In any case adding some driven ground rods tied into the grounding system would be a good idea.
This sounds like you have an electrical system issue. It's not uncommon for building grounds to be bonded to cold water pipes. I ran into something a little similar in the past: How can I diagnose disturbing voltage potentials?
I also once ran into an exactly similar thing at a job once where two electrical boxes held ~20 volts between them and sparked, though I don't know how that was fixed. I remember the phrase "floating ground" being relevant, though.
Diagnosing this will be unpleasant and slow. Start disconnecting everything electrical in your home. Go with the master breaker first, then start removing appliance plugs if the voltage is still there. Keep going until you find the difference in potential between your plumbing and the city plumbing. Something is electrically connecting between the city and your pipes. It may be outside of your "normal" electrical system, though. Something could externally be making a device in your home live and turning the breaker off wouldn't cure it (e.g., landline phone system).
At greater extremes, this could be on the power company with a bad neighborhood transformer (neutral is often bonded to ground) or earth voltage difference that your building is attached to.
Calling the power company and water company are also good methods to solving this.