mike, peter placed a good post re filters and pumps if you are thinking of using creek or river water, if you have a decent size tank on your van (60 litres and above) then free camping for up to a week with cautious use would be achievable, inclucing carefull showers, thats all we use, if you are worried about the ammount of water and your tank is say 60 ltrs, then chuck it and replace it with a 100 or even a 120 litre tank

if you wish to have filtered water in the van then place a "dual cartridge type" filter, the same as you would use at home, somewhere in the line maybe on the drawbar with a hose coming out the other side to fill the tank, the hose could be a permanent fixture running along the chassis and under the van, this would take most impurities out but not the "bugs" so please dont use this type of filter to screen river or creek water, use peters advice and treat that way

we do not use river or creek water, we prefer to carry our own, what we carry in "little blue" lasts a week and if we are going further afeild then we take "squeeky" and we carry 2 weeks supply in there, even with the 40 ltr engel as well as "little blues" fridge we run out of tucker long before we run out of water, worse still the grog supply starts to dwindle and thats a state of affairs that cannot be tolerated at any stage!!

mate dont over complicate free camping, people try to overcomplicate your water, power, food needs, it really is not that hard or complex, if you have enough to stay a week then that is plenty, even up far north it is rare to stay away from complete civilisation for more than a week, you can top up your supply from there,

not too many people want to sit under the same tree for more than three or four days and then we move on, a couple hundred kms up the road and we squat again having probably gone through some sort of civilisation in the meantime, there you can "top up"