We do a lot of boondocking with a 30 gallon fresh water tank. We carry several six gallon plastic "jerry cans" and fill them at campgrounds or ranger stations (always with permission).
The hardest part is transferring the water from the jugs into the tank -- I lift the jugs and pour them, while DW holds a big funnel that we made from a two liter drink bottle. Great exercise!!
There will come a time (soon) when I can't lift a 50 pound jug high enough to pour it into the funnel. At that point we will have to get a 12 volt portable pump.
Since we have only a 25 gallon gray tank, we have to dump once a week, so we refill the 30 gallon tank at that point. So we only have to use our jerry cans once during the week.
Sounds kind of like a hassle, doesn't it? But boondocking is so worthwhile -- I am glad to lift those jerry cans. (Plus it impresses the heck out of DW, so that is a big bonus.)