I have asked to have this moved to electrical. There really isn't much to it. Usually hot water heaters only have the 240 volt heating element. Check the rating of the tank and select the next large rating of circuit breaker and wire. Run 2 conductor with ground. Use a double pole breaker with a contact for each leg of the box. Beware of the breakers meant to give 2 circuits from one leg. Connect ground to ground and the black and white wires to each contact on the breaker. At the tank, connect the black and white to each terminal and ground to ground. Mark the white at both ends with black paint or tape.