I agree with John and Greg: there are Two Separate Services, therefore each Service requires a Grounding Electrode System.
Since there is a Metallic Water Line with minimum 10 feet direct contact with the Earth, this Metallic Pipe must be included in the Grounding Electrode System.
In addition, per 250.53(D)(2), the Cold Water Electrode must be supplemented by at least (1) additional Electrode (typically driven rods or "Ufer").
(the water service & meter is in one and the copper water main runs to the other)
This may require the Grounding Electrode Conductors bonding to the Cold Water Line at the same location (i.e.: both terminate within 5 feet of entrance to the Building), unless the Cold Water Line entering the "Other Building" (the Building without the Water Meter) could be figured as if it was coming in from the Street (min. 10 feet contact with Earth).
Sounds to me that the GEC from both Services will need to Terminate at the same location on the Cold Water Line (within 5 feet from entrance to the Building).
There will only need to be (1) Supplemental Electrode(s) to the Cold Water.
Does this sound right???