How to remove hard water stains from windows.?

Because hard water scale is lime and lime is base, the rules of Ph balancing tell us that anything acidic will remove it. Vinegar works wonders on lime scale, so does lemon juice. Mixing lemon juice and vinegar gives you a super window cleaner that removes grease and hard water scale and smells great. I use one part lemon juice (from a bottle, not from lemon, that becomes too expensive) and two parts vinegar and I use a spray bottle to spray it on. I never water it down, there's no need to. Let the solution sit on the lime scale for a few moments then scrub away. you might need a second spraying. As a bonus the lemon also helps remove grease or oily stains so the widows will be clean and bright. For thick scale a product called CLR, available in the hardware stores dissolves serious lime scale build-up.