Posted by Kevin Vollquartz
White film on dishes almost always comes from one of four things: mineral deposits left by hard water, permanent etching of the glass surface, a dishwasher running short of salt or rinse aid, or the wrong dose of detergent. A dab of white vinegar on a cloth tells you whether it is minerals or etching. If the haze wipes off, it is minerals and you can fix it. If it stays, the glass itself has changed.
How do I tell mineral film from etched glass?
Wipe a dry, cloudy glass with a cloth dampened in white vinegar and look at it in good light. Mineral deposit dissolves in mild acid, so the film lifts and the glass goes clear again within a few seconds. Etching does not, because it is not a layer sitting on top of the glass, it is the glass surface itself made rough and dull.
Two other clues help. Mineral film tends to show up on everything in the machine at once, including plates, cutlery and the inside of the door. Etching shows up on glassware only, usually on the pieces that go through the dishwasher most often, and it often has a faint rainbow shimmer when you tilt it towards a window. Researchers who have studied dishwasher corrosion of glass describe exactly that combination of cloudiness and iridescence, and note that glasses already weathered by age and air are more vulnerable to it.
What are the four causes, and what fixes each one?
The four are hard water arriving untreated, permanent glass etching, a softener that has run out of salt or rinse aid, and a detergent dose that is wrong in either direction. Work down the table until something matches what you are seeing. Most households find their answer in the first or the last row.
| Cause | What you see | Vinegar wipe | The fix |
|---|---|---|---|
| Untreated hard water reaching the dishes (no softener fitted, or no salt reservoir on the machine) | Chalky film on everything, glasses, plates, cutlery and the machine interior, getting steadily worse | Wipes clear | Get your hardness figure from your supplier, use rinse aid, run a hotter programme |
| Glass etching (corrosion) | Cloudy or slightly rainbow-toned glassware, plates unaffected, gets worse over months | No change | Not reversible. Prevent it on the glasses you still have |
| Softener fitted but not doing its job (salt empty, salt light on, hardness left at the factory default) | Streaks and drying marks that come and go between loads, often starting abruptly rather than creeping in | Wipes clear | Refill the salt reservoir, then set the hardness level to your water company's figure |
| Detergent dose or a dirty machine | Gritty residue, patchy film, food specks redeposited on clean items | Partly wipes clear | Correct the dose, clean the filter and spray arms, run a cleaner tablet |
Why does hard water leave white film in the first place?
Hard water carries dissolved calcium and magnesium, and when the droplets dry on a warm plate the water leaves and the minerals stay. The Drinking Water Inspectorate bands supplies in England and Wales from soft (up to 100 mg/l calcium carbonate) through to very hard (over 300 mg/l), with much of the south and east of England at the hard end. If you have moved house and your dishwasher suddenly started producing cloudy glasses, your water is the most likely thing that changed.
Dishwashers are built for this. Most have a built-in softener that runs on coarse dishwasher salt, and Which? puts it plainly in its guide to salt and rinse aid: dishwashers need very soft water to work properly, the salt has to be pure sodium chloride without anti-caking agents, and the hardness level in the settings menu should be set from your water company's actual figure rather than a guess. That setting is the step most people skip. It was set at the factory and nobody has touched it since. All-in-one tablets do contain a softening agent, but Which? still advises topping up the salt reservoir, because the amount inside a tablet is often not enough to keep dishes clear over many washes.
Rinse aid does a different job. It lowers the surface tension so water sheets off instead of beading, which means fewer droplets sitting on the glass to dry into spots. In hard water areas it is not optional if you want clear glassware.
Can etched glass be saved?
No. Etching is erosion of the glass surface, so there is nothing to polish off and nothing to dissolve away. Products sold as a cure generally do one of two things: lift mineral film that was never etching in the first place, or fill the pits with an oil or polymer that washes out again. That is worth knowing before you spend an afternoon scrubbing. What you can still do is protect the glasses that have not gone yet.
Etching is driven by heat, high alkalinity and time in the machine, so the sensible response is to pull all three back. If your glasses are hazing, resist the instinct to add more detergent: cut the dose, use a shorter or cooler programme for glassware, and unload glasses promptly rather than leaving them steaming in a closed machine. Thin, decorative and older glasses are the first to go. We wash those by hand with a solid dish soap bar and accept that a dishwasher is not the right tool for every glass in the cupboard.
Am I using too much or too little detergent?
Both directions cause film, which is why dosing confuses people. Too little and there is not enough builder and enzyme activity to hold soil and minerals in suspension, so they settle back onto everything as a dull grey film. Too much, especially in soft water, raises alkalinity and leaves residue that dries chalky, while also speeding up etching over the long run.
Pre-measured tablets take the judgement out of it, which is the main reason we make plastic-free dishwasher tablets rather than a powder. There is no PVA film to unwrap, they are enzyme-powered, and they are free of dyes and fragrance. One tablet per load, so the dose is the same every time whether or not you are paying attention. The honest caveat: in very hard unsoftened water, no dishwasher detergent on the market fully compensates for the water, ours included. Fix the salt and the hardness setting first, then judge the detergent. You can see the rest of the range in our dish collection.
When is it the machine rather than the detergent?
Suspect the machine when the film is patchy, gritty or accompanied by food specks that were clearly on something else. A blocked filter means dirty water gets recirculated over clean dishes, and blocked spray-arm holes mean whole sections of the load barely get rinsed. Which? recommends cleaning the filter monthly and clearing the spray arms every three months, and notes that blocked spray arms lead to poor dishwashing whatever you put in the dispenser.
Grease and limescale also build up where you cannot see them, in the pumps, hoses and behind the filter housing. That is the job our dishwasher cleaner tablets do once a month on a hot empty cycle: they target the grease, limescale and buildup in pumps, filters and spray arms that ordinary washing never reaches. We run ours on the first Sunday of the month, which is the only reason we remember. If you want the full strip-down, we walk through it in how to deep-clean your dishwasher without bleach.
What order should I actually do this in?
Start with the vinegar wipe, then work outwards from the water to the machine to the detergent, in this order.
- Do the vinegar wipe on one cloudy glass. If nothing changes, you are dealing with etching and the rest of the list is about prevention, not rescue.
- Look up your water hardness with your supplier, then set your dishwasher's hardness level to match.
- Fill the salt reservoir and the rinse aid dispenser, and keep both topped up.
- Pull the filter out, rinse it, and hold the spray arms under the tap to check the holes are clear.
- Run a cleaner tablet on a hot empty cycle, then start the monthly habit.
- Give it three or four normal loads before you judge the result. Existing deposits take a few cycles to clear.
If limescale is a running theme across your kettle, taps, shower and washing machine as well as your glasses, the dishwasher is a symptom rather than the problem. Our complete guide to hard water and limescale goes room by room, and the older post on water hardness and cleaning results covers the background chemistry.
