firstly check the tds of the water that you have, this will determine weather you need a ro system and then a di vessel or two di vessels in a row alone.
if you need a ro system i would recommend getting a 450 gpd one which will be good enough for what you want by far i run a round of 400 customers on one the companies that sell them are adaqua , pure freedom and gaps. next for a di vessel you can use a small di polishing unit the same companies sell these, also buy some tulision resin and a tds meter.
you will want a static tank, if you have any farmers etc around you will be able to get an ibc tank quite cheep, empty your pure water into here and your waste down the drain. buy a transfer pump (dirty water sub pump) people use expensive however argos are fine and this will transfer your water from your holding tank to your barrels or your van tank. for the system you could go with a pure freedom trolly these are expensive, the benifit being that you can take them apart and use them as a van mount if you decide to go that way. as you are running window cleaning as an add on i would buy a big boy backpack from the window cleaning warehouse and strap it to a sack barrow this will save you hundreds of pounds, your pour your barrels into the backpack, people run full rounds like this, it will do great as an add on. as for your most important piece of equipment (the pole) you dont want to go cheap on, there are some good companies out there ie pheonix, gardiners or xline, i would strongly reccomend gardnier pole systems as will most one here, as a starter pole i would go for a clx 25 which will reach most of everything, when you get bigger you can always buy an slx which is more rigid and lighter but the clx is a great pole which you can work all day with, a brush (well gardiners sell loads) extreemes are very good. now to save water i reccomend you buy an aquadapter with the orange pole hose it will stop you emptying the backpack quickly and you can turn the water off with a tug of the hose. i think this should help you
