Hmmm. While the words are not perfectly synonymous, as it pertains to campers I would have thought they were the same thing. I'm intrigued that you have two "clean" water tanks and they are labeled differently.
I am not familiar with your rig, but is it possible that the fresh water goes to your shower, sinks, and commode while the potable water goes to a filtered tap specifically for drinking? Perhaps next to the kitchen faucet?
2011 Georgetown 337
2009 HD FLHTCU
2007 HD FXSTC