Sorry richard, Guess I dont know what im talking about there.
not saying you dont. most people use loads of water, over scrub and over rince, because they think they have to. i used to when i first started off, then i just tried it at home to see what i can get away with on my own windows.
i trust my water and brushes. my water never gose over 002ppm and brushes are cleaned each night.
you would be shocked on how little you need. i tried just a quick spray on the window, turned it of, scrubed it a few times, then rinsed it down. when it was dry there was no spotting or anything left on the window.
not all windows are like that and do need a little more water, but try it at home on a window and see what effects it has when you use less water.