When I climbed under the house over the weekend to adjust my water pressure regulator, I traced the cold water supply line from the point that it enters the crawl space. The plumbing in my house is copper, but it connects to some sort of plastic pipe before it connects to the town's supply line. That means that there is no solid cold water electrical ground.
The problem can easily be remedied by adding a jumper around the plastic portion, but I could not see well enough to determine whether the pipe coming in from the street was metal. The line was installed 22 years ago. Isn't it likely to be metal? I'm probably going to call the town to inquire.
The plumbing in the house was replaced in 1999 because we had Quest pipe, so I trust the plumbers did the right thing connecting to the town supply.