This has killed a few plumbers before. Not due to using it as a ground which is honestly completely safe but due to a faulty water heater that was inadvertently

This has killed a few plumbers before. Not due to using it as a ground which is honestly completely safe but due to a faulty water heater that was inadvertently using the copper pipe as the neutral. The plumber turns off the water and cuts the pipe, then grabs both ends and pulls them apart and now he's got wet hands on both sides of the circuit he just cut.