How to clean glass shower doors with hard water stains?

Removing stubborn hard water stains from glass shower doors requires a specialized approach to dissolve the crusty calcium and magnesium mineral deposits left behind by evaporating water. Because these minerals are highly alkaline, they must be neutralized using an acidic cleaning agent. To begin, spray the stained glass heavily with pure, undiluted white vinegar that has been slightly warmed in the microwave. For vertical surfaces where liquid runs off quickly, you can create a thick paste by mixing baking soda with white vinegar. Spread this bubbling paste directly over the hard water spots and let it sit for 15 minutes to break down the crust. Use a non-scratch scrub pad to work the paste in circular motions, applying moderate pressure. Rinse the entire door thoroughly with warm water, and immediately dry the surface completely using a squeegee to prevent new spots from forming.