In my little city, a lot of the water feed lines into the homes are still lead! If you apply a bunch of current to a lead pipe, it isn’t going to be a pipe for long. My bet would be PVC in Alaska.
S Rummings, it works because of Ohms law: V = IR. All metal has some resistance, even copper. When you flow electrical current through it, the resistance causes the metal to heat up. This is also why you have circuit breakers inside your house wiring too. If you didn’t and you had a short circuit, the wire itself could melt and catch your house on fire.
Power = I*I*R. In a resistive circuit that power shows up as heat. Apply 120volts and a lot of current, and you get a lot of heat. It would be wise to make sure your life insurance policy is up to date before running current through water pipes.