Greg, to answer your question, Fixed buildings on piers fall under article 555. 555 does not address anything specific service grounding. The service is required on shore are identified on floating docks and marinas. The options I can think is either put the service on shore and ground it there, run just the ground back to shore or work with the AHJ and round the ground down the bottom of the water. The latter may require additional approval form jurisdictions. I would imagine typically the jurisdiction stops at the beginning of the pier. It would be a case by case basis with the local AHJ
In general, water is not considered conductive because its not in its purest form. Its the impurities in the water that makes it conductive. I would imagine the chemical composition of the water varies greatly form one moment to the next as the water moves around. Here where I am at, the water can be salty the a few hours later, its fresh water.
In a side note, earlier in this string, I spelled out the difference between the GES and the EGC systems. My intent was only because both systems were talked about in this string. In my personal experience, these two subjects are all too often misunderstood and have confused even good electricians, IMOP, its one of the most important subjects to understand in the trade. Although many of us understand the topic, some don't and with both of them were mentioned, I felt it should be touched on.
Grounding and bonding is just a pet peeve of mine.
