The water we use has been taken back to a totally pure state resulting in it being just pure H20. The water out of our taps contains around 300 parts per million of disolved solids so in this state it is impure. The pure water we use has a desire to get back to its natural impure state. As this water is brushed on your windows it absorbs the dirt and so cleans your windows, a final rinse washes this dirt away leaving a clean sterile surface that dirt is much slower to adhere to, meaning your windows stay cleaner longer.