Hi Andy and welcome to the forum,
A full answer to your post would take a while
But I would reckon on an average window using up about a litre & a half of water, about 15-20 litres per standard semi.
Therefore you could possible do 20-25 houses on about 400l
So far though I have not personally used more than 300l in a single day.
I do one office block, 3 storey that would be the equivelant of about 100-120 standard windows and I go through about 125l in the hour & half it takes to do the job, all of the frames are included too.
When working continuously I am using about 100l per hour.
I'm planning to upgrade to a van shortly, probably an Expert like your own, the 2l TDi version as it has a load rating of 900k In to which I shall put a 650l tank. Some would argue that when all other factors have been taken into consideration, if I go around with the tank full up, add in other gear, poles, myeself, tank full of fuel, then I will be overweight. Perhaps they are right, butthat would be a close run thing I think.
Anyway, I would say to go for the largest tank your van can carry.
Hard water area, definitely R/O system, whether you have a storage tank and transfer to your van, or an all in one system inside the van is down to you.
There is a lot of choice out there, including going the DIY way of Matt.
Gordons also asked about WFP systems, I put these links on his reply, so easier to just post a link to his posting!
http://www.cleanitup.co.uk/smf/index.php?topic=8123.msg60856#msg60856A back pack may well be a good answer to those awkward access accounts, but so is a trolley.
But it is certainly a good idea to have either one or the other to compliment your proposed van mount system.
Regards
Ian
