It just depends upon how long it will sit. I would replace all water if you will let it sit for a month or longer, but if less you probably do not need to do so. I would drain the water tank and also flush some new water through the system and the water heater when you fill the tank for the next trip.
I can tell you if you hook up to really hard water(high iron content) you could wind up getting a sulfur smell (like rotten eggs) and that can be caused by the reaction of the anode rod with the water.iIt would take some time for this to appear and you would have to replace the anode rod to get rid of the smell . LEE
Anodes are only found in Suburban water heaters, but not in Atwood heaters. That is because the Atwood uses an aluminum tank and it is not as effected by electrolysis as is the steel tank of a Suburban. Never use an anode in an Atwood water heater as it will cause problems there.
As far as draining, you should drain any water that doesn't have clorine added as it will allow growth of mold or bacteria in your tank. Some parks on wells don't treat their water so be sure to drain all your water when you get back.