I bought new, so I missed all of the thrills of stuff growing in the fresh water tank, the "black mountain" (petrified pooh) that can grow in a black tank, and mouse poop, mold, etc... that can happen in vintage. I use my fresh water tank if I'm planning to boondock, and have learned to carry 5 gallons in it even if I'm not for an emergency shower after changing a tire, etc.
However, even with a new unit I've chosen not use the fresh tank for cooking or drinking. I carry bottled water for that. My dentist informs me that so many people drink bottled water now that he is seeing an upswing in business due to lack of florine intake. I drink tap water when I'm home and I will put a gallon in my refrigerator before traveling, but Mexico taught me to be wary strange tap water.
Even though most tap water in the USA is fine I prefer to enjoy travel without being accompanied by diarrhea. Over-cautious? Well, is there a downside of not getting Tiajuana tummy?
Use the "search" function here as you're learning about your new toy. It is amazing how much knowledge there is here and you wouldn't believe how many mistakes you'll avoid thanks to the generous people here. My semi-permanent campground has several older women who've found themselves without a mate and without a clue. They now have to learn if they want to keep on camping. It is solely through what I've garnered here that I can really contribute to their sense of safety and freedom.
Now before you proceed further, look up "blue tank"..... which is actually your portable GRAY tank. Back in the 70's it used to be fine to drain your gray water on the ground, but between environmental rules and much more heavily used campgrounds this is no longer acceptable. To camp, you'll need to get a "blue boy" and position it under the gray water drain and tow it to the dump station every few days. (Of course if you're really in the wild and it's a dark night, "thirsty raccoons" can happen.) If you're doing a major restoration of course you can add a permanent gray tank.
The fun never stops... nor the learning.
Happy trails... Paula Ford