Hunter, Carrying a 1/4 to 1/2 full fresh water tank is often recommended. It assures you good water when it is not available where you stop; enables you to stop in places which do not offer hook-ups; gives you a potty along side the road when you gotta go; and in case of storms which might interrupt
water supply (usually campgrounds with their own well, when the power goes off). And if you pull into a campground during a rain, you don't have to fiddle with hooking up--you are fully self-contained.

The basic premise is that you keep your fresh water tank clean at all times--drain it regularly and refill (whatever level you want or may need). Follow Manual  directions for emptying the tank; they differ from model to model. There is also a product called "Drinking Water Freshener" (What else?) put out by Camco and sometimes available at WalMart, but at nearly all RV Supply Stores. It will go a long way toward keeping your water fresh tasting over a longer period, especially if you have the on-board (Everpure) water filter.

Run with empty, or nearly so, black and gray water tanks. I usually have a small amount of water in each with treatment chemical of choice. Good old fashioned BORAX (not Boraxo) in your holding tanks about half full of water, and going down the road, is absolutely the best way to get those tanks squeakyclean! (DO NOT use it in your fresh water tank.)

By the way, if your water heater tank will take it and most will, use the TANKMAN sacrificial anode. It replaces the drain plug near the bottom of the tank. It is magnesium which reacts with calcium and
other chemicals in your water, precipitates these out, and saves your tank from corrosion. It should be replaced about every six months: oftener in real hard water areas, longer in softer water.

Donald