The water piping is bonded to the electrical ground in order to insure that the _water_piping_ has a true electrical ground -- IOW, to prevent the water piping from becoming live in the event of an electrical fault somewhere.
The first poster had it right. The water piping is already at ground because it is in direct contact with the ground. Unless of course you have your water brought to you on pipes suspended in the air. Or perhaps you have it flown in?
Someone already mentioned the words "cathodic protection" with respect to gas pipes.
What that means is that the gas company has connected a low voltage source between a metal anode buried in the earth and the gas main and the pipes leading off it to each user. The purpose is to make the pipes slightly more electrically negative than ground so that they don't get eaten away by galvanic corrosion.
The same sort of active protection is sometimes used at boat marinas and on buried metal structures like guy wire anchors. The systems are also known by the names "active cathodic protection" or "impressed current protection".
There's a dielectric (insulated) coupling somewhere near the gas meter to insulate the gas pipe in your house from the buried main and feeder so that you don't "short out" that deliberately applied protection voltage, because the gas pipe in your home probably gets electrically grounded through some gas appliance it's connected to.
The use of plastic buried gas piping has eliiminated the need for those kinds of corrosion protection systems on new work.
The correct term is "Bonded". The current code as written requires that all interior metal piping be bonded together. This can be accomplished by using #6 copper wire and approved clamps. It is common in New Jersey to bond the hot and cold water pipes together at the water heater location. It would be very easy to continue the bonding wire to the gas pipe at the water heater. Some jurisdictions do not require that the gas pipe also be bonded. Some gas companies do not want their pipes bonded. The electrical inspector would have noticed this and would have failed the job if it wasn't done correctly.
Did the electrician also install at least one (Preferably two) ground rod?
My mother in law's dishwasher developed a short to the incoming water pipe. Most of her water piping is PVC, but some of the outside parts are metal, and NOT bonded to ground.
We discovered this one day when she went to water the lawn while the dishwasher was running. She reached for the faucet, and ZAP! Fortunately, it was not lethal.
No, he didn't. The electrical system has its own, *separate* grounding electrode. Metal water piping is bonded to the electrical system grounding electrodes to ensure that the metal water piping cannot become live, *not* to provide a ground for the electrical system.
BTW... have you ever heard of plastic water piping?
I asked that very same question to the people I shoot with at the range - all of them either are instructors for gas service or perform field repair services for the gas company. Every single one, all 3 of them, said "DON'T DO IT!!!!" shortly followed up by "Mind if we come by this week to INSPECT your service??"
The gas company protects its own piping, if you must use ground wires to plumbing - use your cold water tap. Better yet save your pennies like I am and get grounded service. If I keep saving my extra money I might be able to afford it within the next 20 years - but's that's only if everything else in my life goes perfectly.
Did you find out HOW the dishwasher shorted to the inlet pipe? Seems a bit hard to fathom unless whoever installed the wiring to the dishwaher didn't ground it properly.
A plastic bodied water inlet solenoid valve might have insulated the inlet pipe from the rest of the dishwasher, but how did a switched hot lead contact the pipe? Maybe the solenoid valve's coil developed a short to it's case, which was electrically connected to the piping, but not to the rest of the machine.
Metal water piping burried in the ground cannot become live. It is as well grounded as possible. If you connect the house's ground to it then it is in order to keep the house's ground from being live compared to the water pipe.
As a water source? Never. What has that to do with anything discussed? Nobody is going gto use ploastic for grounding.
There is no guarantee that the electrical system's grounding electrode, and the metal water piping, are at the same potential unless they are bonded together -- despite both of them being buried in the ground. Electrical resistance in the earth is not constant, and in fact can vary widely even over short distances.
I repeat: the *sole* reason for bonding metal water piping to the electrical system's grounding electrode(s) is to ensure that the water piping is at the same potential as the electrical system's ground, so that the water pipes cannot become live in the event of an electrical fault.
Google is your friend, and educating yourself on this topic should be easy.
While both pipes are buried and may be made of metal, only the water line should be used as a ground unless it is fed by a plastic pipe. The gas line should NEVER be used as a ground, although it should be grounded to the building ground, because gas supply lines can also be made of plastic, and even if it is metallic it will have an insulating fitting at the meter to prevent interference with cathodic corrosion protection of the underground lines.
If you have a furnace or a powered water heater and grounded wiring, the connection through this equipment will also ground the gas lines. However, I believe NEC requires a separate cross connection to ensure proper grounding.
So, my question stands: For the same reason that you ground the water pipe so that it is not energized, do you need to do the same thing to the gas pipe source?
Again I am interested both in what CODE says and what is the smart recommendation even if not required by code.
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