The secret is the water. Water that we use from day to day (tap water, spring water etc.) is full of minerals and impurites. Even rain water tends to be. When this water is left on glass, the water molecules evaporate, but the minerals and impurities are left. However, we don't use this impure water.
We filter our water to create 100% de-ionised water. This water is 100% pure. We feed this de-ionised water through our carbon fibre poles and onto your window. We use special brushes to loosen the dirt on your window which is absorbed by the de-ionised water. We then rinse the glass, washing off the dirt. This leaves only the pure de-ionised water. That means that when the water molecules evaporate, it leaves the windows sparkling clean as there are no minerals or dirt left behind. And that's it!