Article 250.104 (B) Where installed in or attached to a building or structure, a metal piping system(s), including gas piping, that is likely to become energized shall be bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor where of sufficient size, or the one or more grounding electrodes used. The equipment grounding conductor for the circuit that is likely to energize the piping shall be permitted to serve as the bonding means.

So if it's required to be bonded, a random water pipe is not legal. Metal water piping are required to be bonded always. Gas pipes are only required to be bonded if they may be come energized. If the heater has an electric control system, I'd consider that as something that is likely to energize it so you could use it's grounding conductor or run one back the building ground rods, service enclosure, or service ground connection.

Ronnatalie, using that logic wouldn't bonding gas pipes be code, most all gas devices use electricity as well?

However the bonding means can also be the equipment grounding conductor of the appliance itself. If you have a gas furnace/dryer/range etc... that is connected to a grounding conductor then the lines are bonded by that connection.

Yes I agree with JMVD.

"...wouldn't bonding gas pipes be code, most all gas devices use electricity as well?"

"The equipment grounding conductor for the circuit that is likely to energize the piping shall be permitted to serve as the bonding means."

It IS BONDED by the equipment grounding conductor supplying power for the devices, and does NOT require any other bonding line.

It should be noted that many gas companies are now requiring the gas piping be bonded to the grounding electrode system with #6 Cu if any corrugated stainless steel tubing (CSST) is used within the structure. The idea is to protect the CSST from damage due to an indirect lightning strike. While not an NEC issue, they can and will refuse to turn the gas on until you comply.

Normel and others...when I posted the question originally that is the one fact that I omitted. In both cases I dealt with there was corrugated steel tubing involved.
So when you say "bonding to the grounding electrode system" do you mean that it can be bonded to a grounded water line? This is the instructions that a certifed and licensed gas installer gave me.

I checked the continuity between the gas pipe and the ground prong on the plug that supplies power to the power vent fan. Sure enough there is continuity so the EGC in the branch circuit is supplying ground.

"In both cases I dealt with there was corrugated steel tubing involved. "

The connections made between CST and other [portions of the system are mechanical connections and many use non-conducting material to achieve a seal.

A problem then occurs if lightning induced transients occur on the CST.

It is not effectively grounded and arcing can occur at the connections as the induced voltages seek ground

You have to remember that every conductor in a time varying magnetic field has currents induced.

If the field is strong enough or changes quickly enough the induced voltages can be very high.

Lightning has BOTH large high amplitude magnetic fields AND rapid changes in the amplitude (tens of nanoseconds rise time and thousands of microseconds decay with an overall duration in the hundreds of microseconds to low millisecond range).

Currents can be tens of thousands of amps, resulting in large magnetic fields.

These are the same induced voltages that can damage LAN equipment at hundreds of yards from an actual strike.