A quick look at the Chic site and it appears that you are in the UK and they sell DI water units. Basically like the water softeners you get from Culligan. Since it is just a cartridge that you put your inlet hose on you can put one of these in just about anything you want including a van. Quite simple it would seem.
Now if you are talking about RO (Reverse Osmosis) water that is a whole nother story because unless you get a huge machine they only put out a small amount of water. Users of RO, which is better than DI by a slight margin, tend to fill tanks overnight and haul the tanks to the jobsite as you can't keep up with water use onsite.
Both systems leave glass "virtually" spotless with a slight edge to an RO machine that has been fed through a DI cartridge.
Hope this helps.