Hard water usually accumulates at the bottom of windows, but it occasionally be found higher up due to rampant sprinklers. Also, silicates my accumulate on the glass from stucco and other building materials surrounding the windows. Because windows (commercial and especially residential) may be fabricated with coatings such as anti-glare, reflective, etc., it is important to choose a polishing method (cleaner and polishing pads) that minimizes the risk of damaging these more sensitive and softer surfaces. This video describes the cautions and tips associated with windows located in the direct sunshine (which can show many glass defects) and those located higher up where viewing is more criticized.
Caution & Tips 1