My 200A main panel ground currently goes to the metal water pipe right where it comes into the building. Presumably the pipe was allowed as the only grounding electrode when the system was installed years ago. But the wire to it is not right – it appears to be three pieces of #10 twisted together, in conduit – so I thought I'd replace it with what's really required which is #4.
However, if I read the code correctly, 250.53(D)(2) now requires a supplemental electrode like a ground rod (or, if necessary, two) when a water pipe is used. And if a water pipe is not used, a ground rod (or two) or other permitted electrode is required anyway by 250.52(A) and 250.53(A). So it seems like the water pipe is useless as a grounding electrode, since you have to install the same other electrodes that you would need without it.
It also appears that 250.104(A) requires bonding the metal water pipe to the GEC using the same size conductor that would be required if it were used as a grounding electrode. The only difference is that that connection does not have to be within 5' of where the pipe enters the building, as would be required if using the metal water pipe as a grounding electrode.
Are these understandings correct or am I missing something here?