I use a spray from Bnq, which is readily available incase I should run out. Spray on, leave whilst do another window and come back scrub n rinse.
I used to have a customer who rinsed his car weekly on his drive with his karcher and constantly sprayed the downstairs bay. I always had a word with him about it, cause he never got it in his thick head that my water is pure unlike his tap water. I even put the price up due to it, thinking this would stop him but sadly it didn't.
Now he cleans his own windows