I have a residential run Iv been doing for 5 years all traditional methods and always said I'd never go wfp. There is quite alot of work that ladders would be easier for and not all windows are accessible by the pole. But I have decided To go for wfp for all the risky and pain in the ass houses and maybe try for commercial work. I was needing some help, How long would 400 litres keeP you working for? And how long does it take to get 400l of pure water? If I was to want 2 poles going at once, how would I go about this? The area I live in has soft to moderate soft water, will just a di setup be ok or will I need the ro? Or will it be better to just test the water myself? What's the reason for different sized di vessels? Also what do you find easier, make pure water in the shed then transfer to van or just put it all in van? Sorry for all the questions, Any advice is greatly appreciated..