i got the wcw backpack and had every intention of using it on my back, but it doesnt last long enough and is very heavy.
i bought a cheap trolly £15
got 2 25liter water drums (for camper vans) £10 each
made a box for the drums and placed in at the bottom of the trolly, the drums slide in and i strap them inplace with one of them elastic hooks, set the backpack on top of that, the 2 drums and the backpack full of water does me about 10 council houses. Its so handy, cost me less than £150, and it performs quite well, better than my van mount by far.