Like many folks how much water I haul around depends.
If were staying at several nice RV parking lots maybe/long trip 1/4 (60 gal tank).
If were traveling in the southwest (water quality issues) and don't know where we will spend the next nite maybe 1/2 tank.....or a full tank when in one location for many days.
Short runs to a nearby COE/state campgrounds where we know we getting good water maybe be 1/8 tank.
Back when our tow truck was a gazz guzzlin' carbed gazz engine with a whoppin' 185-250 hp we seldom traveled with a full tank.
Todays new gen high hp gazzers or the diesel no worries about performance issues or how much water.