Pretty sure that it was a ground fault. The drain pipe was properly grounded. The source pipe was not. An electrical fault in the wall or in an appliance made a short to ground. Unfortunately the ground the that the power circuit was depending on was a connection to the water source pipe. As a result the water source pipe and all the water in it was electrified. In the shower he would have been standing in a pool of properly grounded water (due to contact with the drain pipe) while spraying electrified water on his head. Very fatal situation. Current flowed thought his whole body from head to foot, probably rendering him unconscious instantly, and dead within seconds.