The biggest effect on building grounding systems has been the decrease
> in reliance on metal plumbing, due to the usage of plastic piping.
... which was officially recognized in the 1993 revision of the NEC. Article 250-81 permits grounding through interior metal water piping from a point more than five feet beyond the point of entrance into the building. An exception exists [*] "provided there is qualified maintenance and the entire length of the pipe is exposed."
[*] from the 1999 edition, which is all I have conveniently at hand. I got my books from
formatting link
which are more user friendly
> than the actual code books, which are more like legalese.
It ain't cheap, but a good reference is the NFPA's "National Electric Code Handbook". The base code book (also published by NFPA) would put a lawyer to sleep, but the _Handbook_ quotes the entire Code with interspersed commentary and illustrations.
Joe Morris