Hard water stains look chalky, matte and white to light gray, and they build up as a crust rather than sinking into the surface like a dye. On glass they read as a cloudy film that never wipes clear; on chrome they are white rings and speckles around every water droplet that dried in place. Color matters, because an orange or brown mark is a different mineral and a different fix.
The visual signature
Look at a shower door that has not been squeegeed. Hard water leaves a haze made of hundreds of dried droplet rings, each one a ring of mineral left behind when the water evaporated and the calcium stayed. On a faucet the same process builds a pale scale around the aerator and along the base where water pools. On dark tile it looks like dusty white streaking that returns within days of cleaning. Run a fingernail across it: hard water scale has height and catches the nail, while a stain that has soaked into the glaze does not.
What the color is telling you
White to gray means calcium and magnesium carbonate, which is textbook hardness. Orange, red or brown streaks below a tap or in the tub mean iron, which stains rather than scales and needs an iron filter rather than a softener alone. Black or dark brown specks usually indicate manganese, which travels with iron in many wells. A pink or salmon film in the shower is not a mineral at all, it is an airborne bacterium that grows in damp bathrooms and wipes off with cleaner. Reading the color correctly saves you buying the wrong machine.
Where the deposits show first
Hardness announces itself wherever water dries or gets heated. Shower glass and tiled walls go first because they are wet daily and never wiped. Faucet aerators clog and spray sideways. Kettles and coffee makers grow a rough white lining. Toilet bowls develop a hard ring at the water line that a brush will not shift. Dishwashers leave glassware permanently cloudy, and that cloudiness is often etching rather than deposit, which does not come back off. Water heaters get quieter symptoms: rumbling or popping as scale traps steam under the sediment layer.
Confirming it is hardness
The USGS defines hardness as dissolved calcium and magnesium, and classifies water as soft at 0 to 60 mg/L as calcium carbonate, moderately hard from 61 to 120, hard from 121 to 180, and very hard above 180 mg/L. A test strip or a lab report puts your supply in one of those bands and tells you whether what you are looking at is genuinely a hardness problem worth treating. If the number comes back soft and you still see white marks, look at what is being sprayed on the surface instead: cleaning products and soap scum leave their own film.
Questions people ask about what do hard water stains look like
Are hard water stains permanent?
Fresh deposits dissolve with an acidic cleaner such as vinegar or a commercial descaler. Long-standing scale on glass can etch the surface underneath, and that etching is permanent even after the deposit is gone.
How do I tell hard water stains from rust?
Color and texture. Hard water scale is white or gray and sits proud of the surface; rust from iron is orange or brown and stains into the finish, and it responds to different cleaners.
Will a water softener stop the stains coming back?
Yes for calcium and magnesium deposits, because the softener removes the minerals before they reach the fixture. It will not stop iron staining, which needs an iron filter as well.
Why is my glassware cloudy even after the dishwasher?
Hard water leaves mineral film on glass as it dries, and over years the combination of hot water and detergent can etch it. Softened water plus a rinse aid prevents new film forming.