Well it really depends on how paranoid you wanna be about it.
I have two filters in my bus, both of which are washable Metal Mesh. The first is a 30micron filter, and the second is a 10micron filter. I also filter before putting into the tank.
Alot of the times I filter on the go, I also dont have alot of money to keep buying all these filterbags and disposable filters and such. PLUS YOU CREATE WASTE, when you do it that way.
My filter system has been working good, although its possible I dont get all the water out. However, I do tend to use fuel that is pretty good, and am rather selective.