Hard water stains are mineral deposits left behind when water evaporates, mostly calcium carbonate, and they respond to chemistry rather than effort. Mild acid dissolves them; scouring only scratches whatever they are sitting on. Knowing which acid is safe on which surface is most of the job, and preventing them coming back is a separate decision entirely.
Dissolve, do not scrub
The USGS describes hardness as dissolved calcium and magnesium, and what you are looking at on the glass or the tap is those minerals left behind as the water dried. That deposit is soluble in mild acid. White vinegar is the standard household option, applied wet and left in contact long enough to work, which usually means a soaked cloth wrapped around a tap or laid on a shower screen rather than a quick wipe. Commercial descalers work faster on heavy build up. In every case, contact time is doing the work, not pressure.
Surfaces that acid will damage
Natural stone is the important exception. Marble, limestone and travertine are calcium based themselves, so vinegar and descalers etch them permanently, leaving a dull mark worse than the stain. Use a cleaner made for stone instead. Acid also damages some brushed and coated tap finishes, aluminium, and the seals on older fittings if left too long, so test on a hidden area and rinse thoroughly afterwards. On glass, avoid abrasive pads: fine scratches hold future deposits and make the next stain harder to remove than the last.
The awkward places
Shower heads are best unscrewed and soaked in descaler or vinegar overnight, which clears blocked jets nothing else reaches; where they cannot be removed, a bag of vinegar tied around the head does the same job. Kettles and coffee machines have their own descaling routines worth following rather than improvising. Toilet bowls hold deposits below the water line, so bail the water down first or the descaler is simply diluted. Glass shower screens, once clear, stay clear far longer if squeegeed after use.
Stopping them coming back
Cleaning treats the symptom. On the USGS scale, water above the hard band deposits fast enough that no cleaning routine keeps up, and the durable answer is to remove the hardness with an ion exchange softener so nothing is left behind to dry. Where a softener is impractical, a filtered shower head with a squeegee habit helps at the fixture, and drying surfaces after use helps everywhere. Our hard water shower head guide covers the point of use options and what they genuinely change.
Questions people ask about how to remove hard water stains
What actually removes hard water stains?
Mild acid dissolving the mineral deposit, given contact time. White vinegar or a commercial descaler held against the surface, not scrubbing.
Is vinegar safe on all surfaces?
No. It etches marble, limestone and other calcium based stone permanently, and can damage some tap finishes. Use a stone specific cleaner there.
How do I clear a blocked shower head?
Unscrew it and soak it in descaler or vinegar overnight, or tie a bag of vinegar around it in place, then flush the loosened deposit out.
Can hard water stains be prevented?
Only by removing the hardness with a softener, or by drying surfaces before the water can evaporate. Cleaning alone treats the symptom.