In north america both terminals of the heating element are galvanically isolated from the tank, so this is not an issue if the wiring is installed with due car

In north america both terminals of the heating element are galvanically isolated from the tank, so this is not an issue if the wiring is installed with due care. In countries like brazil and germany that allow "bare wire" heating elements you might have trouble with the tank lining plating onto the element or visa versa.