Hard water stains are left by minerals such as calcium and magnesium in tap water. These stains can build up and even penetrate materials. If left long enough, hard water stains can become permanent, leaving a white or brown stain on sinks, faucets, shower doors and countertops. There are many products for cleaning natural stone and quartz countertops and Silestone, but you could also use white vinegar. Vinegar is a mild acid and dissolves the lime scale and calcium deposits that make up hard water stains.
Mix distilled white vinegar and water at a rate of one part vinegar per three parts water. Pour into a spray bottle.
Use a soft cloth to buff the stain, wetting it with the vinegar mixture whenever it gets dry. Tough deposits will need more care, but this will take care of new and light stains.
Wet a cloth with vinegar and place it over the stained area. Thoroughly saturate the area. Leave it for about 15 to 20 minutes to give the vinegar a chance to dissolve the stain.
Scrub the stain gently with a soft-bristled toothbrush. Spray on the vinegar and water cleaning solution as needed.
Repeat steps three and four until the stain is removed. Some hard water stains may be permanent, but these steps will often reduce them.