For extreme hard water stains, Pour a little baking soda on the tough spots first, let it sit for 5 mins and rinse before doing this remedy. Fill a spray bottle 1/2 full with vinegar. Add 1/4 cup lemon juice. Fill the remaining space in spray bottle with soap of choice. Shake up that bottle and soak those stubborn stains baby. Let sit for 30 mins. Time to scrub that grime away.