Meaning bonded to the piping system that does have the GEC, correct? I'm a little unsure myself, but with the way I read the first sentence in 250.50 is that if the two piping systems are completely separate, then you must bond them together (perhaps with a GEC to both) because they are two different electrodes. If the piping systems are connected together, you're good. Yes? There's the exception for difficult to access CEE, but not for metal piping.As long as the remote piping system is still continuous metal and bonded, you should be okay.
I would start where one water feeder splits into two services, maybe at the meters. Depends on how your locality serves water.So I will need to determine if the two piping systems are connected at some point.