Assume this to be a Service not a "feeder" for a residential problem. The size for the ungrounded conductors could be #1 AWG and the size for the grounded conductor should not be not smaller than #6 AWG. The overcurrent protection would need to be 150a maximum. The GEC to the water would be #6 AWG and I don't find a code rule that says you need two rods. Bonding of the piping systems is required but I don't see where in the code that it has to be at the water heater. All conductors are considered to be copper. These conductor sizes are only valid for residential. If this is a non-residential problem the sizes will be larger.
And another thing- I don't see in the code that you need to use a rod.
I feel much better now that I've vented
[This message has been edited by George Little (edited 10-29-2005).]