The short answer
Hard water stains are minerals left behind when tap water dries on glass. Soak them with a mild solution of white vinegar in water, leave it for a few minutes, wipe gently with a soft cloth or non-scratch pad, rinse well and dry. Test a small area first, keep vinegar off timber, stone and tinted film, and never use scouring pads or strong acids. If the glass still looks cloudy and feels rough, it may be etched, which cleaning cannot fix.
What hard water stains are
Tap water carries dissolved minerals. When a drop of water dries on glass, the water evaporates and the minerals stay behind as a white, chalky spot. Over time, spots overlap and build into a cloudy film.
They are not dirt, so ordinary soapy water does little. They need a mild acid to dissolve them.
Where they come from in Maltese homes
In Malta and Gozo, hard water spots usually come from:
- Washing the balcony or terrace with a hose or bucket, splashing the windows and balustrades.
- Garden sprinklers and plant watering near glass doors and balustrades.
- Drips from roof water tanks and air conditioning units above windows.
- Rinsing windows with tap water and letting them dry in the sun.
- Shower screens, which get wet every day.
This is why professional cleaners use purified water on the outside of windows. See how water-fed pole cleaning works.
Hard water stains, salt film or etching?
Three problems look similar but need different approaches:
- Hard water stains: white spots or rings, often in a pattern where water dripped or splashed. They feel smooth or slightly gritty and soften with a mild acid.
- Salt film: a fairly even, misty haze on sea-facing glass, from sea spray. It usually rinses off with plenty of clean water. See our guide to removing salt from sea-facing windows.
- Etching: a dull, frosted or cloudy patch that stays the same whether the glass is wet or dry, and feels slightly rough. It is damage to the glass surface itself, and no cleaning will remove it.
A quick test: wet the area. If the cloudiness almost disappears while wet and comes back as it dries, it is probably deposits that can be cleaned. If it looks the same wet or dry and feels rough, it is probably etched.
How to remove hard water stains
What you need
- White vinegar and water.
- A spray bottle or bowl.
- Soft microfibre cloths, and a non-scratch nylon pad for stubborn spots.
- A squeegee and clean water for rinsing.
Step by step
- Clean the glass first with mildly soapy water, so you are only dealing with the mineral spots.
- Make a mild solution of white vinegar in water. Start weak. You can always make it a little stronger for stubborn spots.
- Test a small area, especially on coated, tinted or decorative glass.
- Apply and leave it to soak for a few minutes. On vertical glass, a cloth soaked in the solution and held against the spot works better than a quick spray.
- Wipe gently with a soft cloth, or a non-scratch nylon pad for stubborn spots. Let the solution do the work rather than pressure.
- Repeat if needed. Heavy build-up may take several rounds.
- Rinse thoroughly with clean water, and squeegee or dry the glass straight away so new spots do not form.
Keep vinegar away from
- Timber frames and gallariji, which it can mark.
- Limestone sills and stone surrounds, which acids can damage.
- Tinted or reflective window film, unless the film maker says it is safe.
- Metal fittings on balustrades, which should be rinsed and dried if any solution gets on them.
Windows and glass balustrades
Spots on outside glass and balustrades usually come from balcony washing or sprinklers. Treat them as above, working from the balcony side only. Never lean over a balustrade to reach the outside face. See our guide on how to clean glass balustrades.
Shower screens
Shower screens get the worst of it, because they are wet every day. Treat the spots as above, then:
- Squeegee the screen after every shower. It is the single most effective habit.
- Leave the door open so the screen dries quickly.
- Clean regularly before deposits build up.
Solar panels
Solar panels can also get mineral spots, usually from being rinsed with tap water in the sun. Check your panel manufacturer’s cleaning guidance before using anything other than water. Most recommend plain water, ideally purified, and a soft brush, early in the morning while the panels are cool. See our guide on how often to clean solar panels in Malta.
What never to use
- Scouring pads, steel wool or abrasive sponges, which scratch glass.
- Razor blades on coated or toughened glass, which can scratch it.
- Strong acids or heavy-duty descalers not made for glass.
- Bleach, which does not dissolve mineral deposits.
- Mixing cleaning products, which can release harmful fumes.
How to stop stains coming back
- Do not let tap water dry on glass. Squeegee or dry it after washing the balcony or watering plants.
- Point sprinklers away from glass doors and balustrades.
- Fix drips from roof tanks, pipes and air conditioning units above windows.
- Clean regularly, so spots never have time to build up.
When to call a professional
Book a window cleaner when stains have built up over months, cover a lot of glass, or are on glass you cannot reach safely. Professional cleaners use purified water, which has had the minerals removed, so it dries without leaving new spots. They can also tell you whether glass is etched rather than stained.
clear.mt arranges window and glass cleaning across Malta and Gozo. Send a few photos for a free quote. For everyday cleaning, see our guide on cleaning windows without streaks.