Try this it really works:
after I have washed down all the frames and glass with wfp I put it all away and then get my ladders out. What I do next is amazing. I fill a bucket up with soapy water (fairy liquid will do) climb up my ladders and mop the windows. Next I use a squeegee and blade all the bubbles off.
My customers love it. I'm the most expensive window cleaner in England but have the most customers.
Try it.
Can't work out why I spent ten grand on a pure water system though. Must be a reason but I can't remember.