Hard water spots on glass and fixtures

Why the spots come back

Hard water carries dissolved calcium and magnesium. When a drop of it dries on glass, steel or tile, the water leaves and the minerals stay. That is the spot. The U.S. Geological Survey lists spots and film on glassware as a common sign of hard water, and it notes that heating the water leaves scale behind as well.

Every shower, every dishwasher cycle and every rinse of a faucet adds a little more. Wiping clears the layer that is there. It does not change what the next drop leaves.

What the white residue is

• Mineral spots and film. Calcium and magnesium left behind when water dries. Dishwasher makers describe white film on glassware and on the inside of the machine as mineral build-up, most often in hard water areas.
• Soap film. The USGS says soap reacts with the calcium in hard water to form soap scum. That is the cloudy film on shower doors and tubs.
• Detergent film. Not everything white is hardness. GE's support page says phosphate-free dishwasher detergent can leave a milky film on glassware too, and that it is most often seen where the water is hard. So the film on your glasses can have two causes at once.
• Etching. Deposits left long enough can change the glass surface itself. Two glass-restoration companies describe it as a rough, hazy surface that cleaning does not remove. Spots wipe off. Etching does not.

What helps

• Dry glass and fixtures after use. A spot is a drying drop. Wiping a shower door or faucet dry before the water evaporates leaves nothing to spot.
• Use the dishwasher's own settings. Dishwasher makers publish steps for white film: a rinse aid, a vinegar rinse, a citric acid cycle or a dishwasher descaler. Bosch's manual says to set the rinse aid by your water hardness, and Bosch recommends its descaler a few times a year to remove hard water deposits and limescale.
• Check the finish before you reach for a descaler. Kohler's warranty lists acids among the cleaners that void it. Moen's excludes damage from abrasives, alcohol and organic solvents. A descaler that clears the crust can damage the faucet, so read the care instructions for your finish first.
• Treat the water, if you want the cause gone. A water softener removes the hardness minerals, so there is less to dry on the glass. It is not allowed everywhere. Some cities and sewer agencies restrict salt-based units, and your options depend on your address. See water softeners and conditioners and the city pages.

What does not fix spots

• More cleaning. It keeps the surface clear for a day. It does not change the water.
• A salt-free conditioner. It changes how minerals form scale, so there is less build-up inside pipes and heaters. The minerals stay in the water, so spots on glass and film on shower doors continue. See salt-free water conditioners.
• A carbon or sediment filter. These take out chlorine, taste, smell and particles. They do not remove hardness. See whole-house water filtration.
• A drinking-water system at one tap. A reverse osmosis system treats the water at the tap it is installed on. It does nothing for the shower door or the other faucets.

Start with the free water analysis

Before you pick a fix, find out how hard your water is. The free water analysis is done at your tap. It looks at hardness, chlorine and total dissolved solids, and it is not a health screening. You see your numbers first, then you decide.