We use the Unger HydroPower DI Pure Water Filter which is ideal for cleaning your windows.
Water contains minerals, the same as mineral water. You can see those minerals when the water dries. Your bath/shower tiles are a good example for that. The Unger HydroPower DI Pure Water Filter removes those minerals. The removal of those minerals gets the water in an unnatural status. The pure water is searching for minerals and attracts dirt like a magnet.
The result: Totally clean windows without any streaks.
For smaller windows we use the Karcher cordless which is fantastic.