Ok mate, at what point does the water become pure? I read somewhere if you run out of water you can just fill it up again, i'll be honest what i was thinking was start off with a 250 litre system to build the work up then upgrade as i see profits rising, i still have my other trad work to keep me going inbetween going to do wfp jobsIMHO you need to buy the right kit so you can do the job. This needs to take future growth into consideration. It also needs to take other things into consideration as well. For example, you may start wfp because you need to safely clean those top windows from the ground but you will continue trading the downstairs windows.
However, you will quickly find that it is quicker to pole all windows but you haven't got enough water capacity to do this. Now your system isn't an asset to you, its throttling you as your growth is being restricted by your equipment.
We have found that to do a good days work you need to have a 500 liter tank on your van as a single operator. Most days you will use between 350 and 400 liters - great, but you have more if you need it.
An Escort van isn't big enough to carry that so its a waste of time getting one. If you have a 600LX Berlingo/Partner van, then you will find that that is also too small. You need an 800 LX Berlingo/Partner or a LWB Transit Connect T220 or T230. If your Combo van doesn't carry the weight its useless to you no matter how good a condition it is in.
When you start wfp the equipment needed and its application seems so complicated. I bought a fully working wfp trailer with r/o and that's how I learnt. But it was a waste of money. I ended up with a SWB Citroen Relay and TBH it's probably too small for the 2 of us with a 650 liter 2 man system on board.
If I was younger and had a lot of working years left, then I would look at a LWB 3500kg van.