If your water is pure and your brush is clean, it must be something on the windows.
I had a job a few weeks ago, went back next day and they looked terrible, someone asked if a road nearby had been resurfaced and funnily enough it had been! A path very near, si maybe something like that. Look for the obvious.
I didn't use Ionics brush when mine messed up, but I do use Ionics most of the time and best in my opinion.