I always have two filled 5-gallon water jerry-cans on the front deck of my OFF-ROAD POPUP trailer. I also carry two 7.5 gallon AQUA-Tainer totes for capturing grey water with.. Our cassette pottie has its own 6-gallon tote with wheels for black water..
We are also fresh ground bean coffee lovers so to get the same taste everywhere we go we have to bring our brand of bottled water for the coffee... Always a couple of 1-gallon jugs of that on-board all the time.
We use the same bottled water for drinking and cooking with. The fresh water tank is just for washing dishes and showers and squirting squirrels.
This is what we all got used to doing over the years. no real reasons I reckon...
Cycling all of the different water totes is a daily chore for me when camping off the power grid places.
I also carry a 5-gallon jerry-can of gasoline
Roy Ken