Stains on the glass around your home are unsightly. Worse yet, they can etch the glass and cause permanent damage to it. The most common glass stains are caused by hard water deposits. The minerals in the water---usually calcium and magnesium, and sometimes lime and iron---accumulate on glass shower doors, windows, even on glass blocks. You can clean the glass and make it sparkle again with some products you probably have on hand.
Clean light water stains from glass with full-strength vinegar. Fill a spray bottle with vinegar. Spray the glass and allow the vinegar to sit a few minutes. Then, wipe the stains off with a lint-free cloth. Spray any leftover stubborn stains with additional vinegar. Then, rub them with a scratch-free scrubber. Wipe the glass clean with a dry cloth.
Sprinkle a little Bar Keeper's Friend on a wet---but not dripping---rag. Lightly rub the cleanser on the moderate glass stains. Don't rub too hard or too long on one spot or you could mar the glass. Apply more cleanser and re-wet the rag as needed. After the stains are lifted, rinse the rag out well. Then, rinse the glass thoroughly. Wipe the glass dry and buff it with a clean cloth.
Remove resistant stains from glass by using window cleaner and a razor blade. Spray the glass with a window cleaner. Allow it to set a few minutes. Then, carefully use a razor blade to scrape the glass clean. The task will be easier if you hold the blade at an angle as you remove the stains. Spray more window cleaner on the glass as needed to keep it wet. Once you remove the stains, spray the entire glass again. Wipe it clean with a dry cloth.
Never use highly abrasive cleansers or rough scratchers to remove stains from glass. Be careful when using a razor blade to remove stains. The blade is sharp---don't cut yourself---and don't scratch or etch the glass.