Ian_Giles has recently shown me his RO set-up.
You need an outside tap and connect the RO unit:
See here:
http://www.ro-man.com/shop/product_info.php?products_id=33To it. It filters your tap water into a large water container; for example a water butt.
This can take 24 hours to get a water butt full; depending on your RO (so I believe). You'll then fill up a number of manual handling water containers to transport your pure water to where you're going to be cleaning.
Carefull not to overload your vehicle. 1 litre of water = 1 kg.
Along with the back pack you'll need to purchase a brush and pole.