Most of our trips are 3-4 days and we're boondocking. So I fill up at home. This way I know the source of the water and I'm not looking for water at the destination.
On extended trips, I try to fill WHEN I dump, but not WHERE I dump. I've seen too many not healthy things happen to the spigot near the dump station.
I'll ask if there is a spigot nearby when I buy gas, groceries, food etc.
In campgrounds where I'm not getting hookups, I'll fill in an empty full serve camp spot. Or sometimes an extra length of hose is needed and maybe a "water thief" too.
Norm