Hi Justin,
I have a feeling that english may not be your first language, so if you don't understand anything just ask.
The average flow rate for van mounted wfp system can be anything up to 5 Litres per minute. So an hour's work with some switching on and off might consume 100 litres.
RO water will dry on windows and leave no residue. However, sometimes the first couple of cleans on a house that's only ever been done the traditional way may not be up to standard. It is usually necessary for RO water to be "polished" with some kind of de-ionizing resin before use to bring the TDS down to zero.
Your question are a little bit general, you might find you get more response in the "starting a window cleaning business".
Also, other's might disagree with me, but I think there is a distinct advantage to mastering window cleaning the traditional way first, then moving to a pole system.
Mike Boxall, is it allowed to give a link to peter's FAQ about wfp's? I think it would help in this case, but I understand if you don't like it.
Silly