If you're thinking about starting a round then I'd try not to mix the two styles, go WFP from the start. 5x 25ltr barrels in the back and that should see you through 10 houses. I'd not bother with a back pack either, build a good trolley and you can use it as a car mount system unless you need to go walk about.
You will have to make the pure water yourself at home, you can get a half decent system and DI vessel for about 300 notes I think, then you just need a storage tank at home.