Water!
If you've ever used your garden hose to blast the dirt off difficult-to-reach windows you could have done more damage than good. The windows may look clean while they are still wet, but once they dry, all you're left with are dirty streaks.
Airborne particles
Particles from car exhausts and pollen are just two of the things that can cling windows that haven't been cleaned properly.
Grease and steam
Kitchen windows can be the hardest hit when it comes to attracting dirt. Grease and steam from cooking can stick to the glass like glue and can be difficult to remove.
Pets and kids
Your clean windows don't stand a chance when it comes to pets and small children with sticky fingers and paws.
DIY cleaning solutions
Unfortunately, it's often improper cleaning in the first place that attracts even more dirt. Clean glass is very hard for anything to bond to, but any residue left from previous cleaning attempts will attract dirt like a magnet.
Perth water is slightly harder than average, so it is important that windows are cleaned correctly. If not, minerals can stain and even damage the glass and window hardware over time. Your local window cleaner has the correct equipment and training to clean your windows expertly and safely, so there is no damaging residue left behind.
