Wash the windows with car glass cleaner and a microfiber cloth
Dry the glass completely with a clean microfiber towel
Apply white vinegar to a microfiber cloth and wipe the stained areas
Let the vinegar sit for a minute on stubborn spots
Rinse the glass with clean water and dry it again
Use a clay bar on the glass for mineral deposits
Apply a dedicated water spot remover for automotive glass
Buff the windows with a clean, dry microfiber cloth
Repeat the process if stains remain
Finish with a glass sealant to help prevent future water spots