Most of us have double pane glass windows, these help with the energy efficiency of your home. In between the panes is a gas that lasts about 10 years that blocks the elements.
You may be tempted to you a garden hose with a sprayer when cleaning the exterior of the panes but this is not recommended. The force of the glass can damage the seal and dissipate the gas in between the panes. When this happens the windows age more quickly and you will see the stars or fuzzy areas begin to show in less than the 10 year warranty.
It is best to use a window cleaning service or a squeege and materials meant specifically for window cleaning to prolong the life of your windows.