According to Tom Horne :

250.50 Grounding Electrode System.
....
250.52 Grounding Electrodes.
(A) Electrodes Permitted for Grounding.
(1) Metal Underground Water Pipe.

.....

There is no way you can read NEC section 250-50 that allows you to avoid
using the underground metal water piping as part of the grounding
electrode system.

Actually, one can show that very easily: note (A) above:

"Electrodes PERMITTED for Grounding".

Emphasis added.

It doesn't say it's "REQUIRED if present" for use as a grounding conductor.

It says it _can_ be used as a grounding conductor (and elsewhere says if used
it needs to be supplemented).

Elsewhere in the code it goes on to say that such pipes MUST be grounded.

Which means in the end it doesn't matter, because it's going to _act_ as
a grounding electrode, whether the NEC thinks of it as that or not.

This whole argument is silly - it doesn't matter which way, because it's
going to be grounded (and in intimate earth contact giving decent duty
as an electrode) ANYWAY.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.