We recently had the misfortune of finding a water pipe by running a nail through it. To make matters worse, the pipe was under a floor overlaid with tile backer board. Faced with blindly destroying the floor in search of the nail (the ceiling below was already finished), I hit on the idea of finding the leak electrically.
I got out my volt meter and set it to the resistance mode. I grounded one lead to a water pipe and then probed each nail head with the other lead. When I found the culprit nail, the circuit was complete (consult your electrician if you’re at all in doubt about how this works). The happy result was that we were able to make a minimal hole in the floor for repairs.
Jim Albertson, Longmont, CO