Makes a difference on where you are in the country. SW, esp CA, forget finding water, SE, hoses are everywhere and the term "wasting water" is not a thing because water comes out of a river or lake, then goes back into the same river or watershed further downstream... lol.
NE area I find fewer outdoor spigots due to harsh cold winters.
WI is nasty water that will ruin your tanks.
Fill up where you find water. You really do need a much, much bigger fresh tank if living off grid like this. A bus will handle the weight and you likely have lots of room under the floor for giant tanks.
A Jerrycan filter like this
Jerrycan Lifesaver will let you get water from any source, lake, river, sketchy tap, but it is 5 gallons at a time. You can use out of the can or drain it into your fresh water tanks and repeat as needed.
For a bus and your situation I would have a 100 gallon capacity at least. I had a class-c with 65 gal tank, and could go a long time between fills.
