I'm looking at starting the switch to wfp in the next few weeks by buying a backpack system and using it on awkward upstairs windows, then slowly moving on to all upstairs, moneys tight and cant afford a van so usong my estate car and was wondering a couple of things... 1. How much water would I need to carry a day. Will be using 25l jerrycans so how any do you think I'll need. 2. What's the most cost effective way to make pure and what size system would I need 3. Would this be an adequate backpack for the job Big Boy Backpack & RENEGADE Deal Any advice would be well received.