Well you are going to need a water tank for your purified water. If its going in a van, make sure it is baffled. (and not just confused
)
The purification system.
Most would recommend an R/O system, don't forget the pre filters. And then the D/I to polish off the water to 0.000 TDS
A TDS meter, either in line or hand held.
A set of extention poles, what you get depends on the depth of your pocket.
The 6ml pole hose.
50m (or more) of anti kink standard hose.
Hose reel.
Brush head, lots of choice there, and opinions differ on whether to go for a 'flocked' bristle brush, or single filament one.
Water jets for the brush, either the 'needle' or 'fan' jet types.
Various conectors for going between the 2 different diameters of hose.
A pump, various choices there.
Battery, go for a leisure battery, at least 85ah
Flow valve to regulate water flow from pump.
Well that at least gives you a start.
There are a few on the forum who have built their own systems, they will give you further input.
you will need to decide what type of system to go for with regards to hooking up your chosen pole to your brush too.
It will also depend on whether you are talking about a van mount, a trailer mount, or a trolley mount, and not forgeting the Backpack either
have fun,
Ian