For best results, Barrett recommends gently wetting a washcloth in water (yes, more water) and dabbing the water-stained area. From there, dip one end of the washcloth in vinegar and gently rub it on the fabric to remove the stain.
Consequently, what will remove water stains?
Remove Hard Water Stains with Vinegar
Mix equal parts white vinegar and fresh water in a spray bottle for an excellent bathroom cleaner that can be used liberally on showers and tubs. Fully saturate surfaces and let the vinegar solution sit for at least 15 minutes. Wipe clean with a clean, dry microfiber towel.