Removed many code revisions ago.
Ground wires must be run with circuit conductors to the panel.

Is it stil permitted to run a wire from a water pipe to ungrounded two-prong outlet?

You can't run the ground wire to just ANY water pipe. You CAN run it to the main water pipe within 5' of where it enters the building -- IF that portion of the pipe serves as the grounding electrode for your service. [250.130(C)(1)]

Per 250.130(C) you can run it to either:
(1) Any accessible point on the grounding electrode system as described in 250.50
(2) Any accessible point on the grounding electrode conductor
(3) The equipment grounding terminal bar within the enclosure where the branch circuit for the receptacle [...] originates
(4) For grounded systems, the grounded service conductor within the service equipment enclosure

Single ground wires run for the purpose of replacing ungrounded receptacles with grounded receptacles do not have to be run with the other circuit conductors.

Hi,
I don't mean to hijack this thread, but the question I have is directly related.

Quote:
Per 250.130(C) you can run it to either:
(1) Any accessible point on the grounding electrode system as described in 250.50

**Does that statement mean that I could use the EGC from another circuit, (i.e. an accessible recep with EGC), and pigtail them together to form a compliant connection? I want to replace a two prong recep with a three prong ground type.(120v)

(Note that I inquire about the connection of the EGC to a different branch circuit. Both originate in the same panel. EGC wire size will be matched to the same size as the one I want to connect it to. For some reason, there are two recepts in close proximity, on seperate circuits. Neither are kitchen or multiwire circuits, just typical wall recepts. )

Thanks.........and great forum!
Bob

I would not attempt to create an ersatz ground system by even running to the electrode, let alone splicing a wire tied to the GEC.
It says to the GEC system. As in all the way to the actual electrode or GEC.
It is needlesly dangerous in almost any case to seperate the ground wire from the circuit conductors.
The inducatnce of the loop created will slow the response time of overcurrent devices, and can even prevent them from tripping depending on what material is inside the loop.

Do not forget that you MUST provide mechanical protection for the ground wire you run, unless it is large enough (#6 or larger).
Installing conduit (of any type) to protect a single wire is a real PITA, and #6 is a little pricey.
If you hit a large supply house you may be able to purchase MC with a single grounding conductor, but I have not seen it in a few years.

Also, with the increasing use of plastic pipe, the water line is not always a reliable conductor any more. In our city, nearly all water service that has been installed since about 1990 has been done with non-metallic pipe.

the water pipe is not part of the GEC unless it is fulfills the code description and requirement to make it such.. Other than that, any metallic piping is simply bonded as a safety matter.

Samneric has the specifics down but brickeyee does bring up a good point as well.

The new EGC does not have to be run with the other circuit conductors but it must be a cable listed to be run without conduit or it must be in conduit.

That makes the retrofit install difficult and costly. It is almost easier to simply run new cable totally since that is effectively what you have to do for just the EGC.

So, the answer to your actual question is;

yes, if the water pipe is part of the GEC and you attach within the first 5 feet of exposed pipe.

No, if the water pipe is NOT part of the GEC