Thanks for your replies. I was thinking it would cost me more, maybe I have been looking at the wrong systems for what I need.
With the set up windiewasher has suggested, can this be simply mounted into my van, run a hose into the tank, purify the water and away I go as easy as that? As you can tell, a complete novice!
If I filled a 400l tank at start of week, would it last for upto 10 hours and would the water stay pure?
Thanks once again.