Cleaning hard water off your windows can be a difficult task. Hard water spots are caused by minerals in the water being left to dry on the glass. Water evaporates from the glass leaving the minerals behind. Sprinklers commonly spray windows leaving these hard to remove spots behind. The deposits are typically alkali so you need an acid to remove them. There are a lot of household products you can use to remove these spots.
One method is to make a vinegar solution that is one part vinegar and one part water. Mix this together in a spray bottle and then spray it on the spots. You will want to allow the solution to soak for a while and even reapply a few times to help completely remove the deposits. Saturating a towel is another option you can use to keep the solution on the glass while it soaks. Then you can scrub gently with the saturated towel. Do not scrub hard because the deposits can actually scratch the glass. Finally you will spray water on the window and then dry it off with a towel or a squeegee.
Lemon juice is another option you can use instead of vinegar, you can even use half a lemon to scrub the glass. White toothpaste is also an option for removing hard water deposits from glass. Baking soda and vinegar can be used on difficult to remove spots and some people use bar keepers best friend to aid in the removal of spots.
Cleaning hard water spots is not as challenging as you may think if you have the proper materials. A professional window cleaner can help remove more stubborn spots if you are having trouble or cannot reach the spots.