Let me say that I have not been responsible for the arrangement of services as large as yours are likely to be. Having said that are not the basic principals the same regardless of the size of the two services involved?
It would seem to be completely impractical to isolate these buildings from each other electrically.
Since the water supply to the building you are concerned about is not underground the connection in that building is a bonding connection rather than a grounding electrode connection so it need not be within five feet of were the piping enters the structure.
If a single emergency electrical supply is used for both buildings then I suspect that four pole transfer switches are in order to avoid grounding the neutral on the load side of the service disconnecting means during normal operation from the utility supply.
I hope that the reinforcing steel in the footer of that building was made available as a Grounding Electrode. If the footer has yet to be back filled you might consider a ground ring. My concern with the electrode quality is that having markedly higher impedance to ground in one building relative to another building that shares the same metallic water supply is not a great idea. Maybe I'm just a nervous Nellie but I would test the grounding in that second building to make sure that it is not wildly different than the one were the water pipe comes out of the earth.
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Tom
