Salty Water by the Window in Winter: The Aluminium Foil Trick Alternative

The first time I noticed it, I genuinely assumed my neighbour had left something out after making dinner.

There was a plain white bowl on the windowsill, holding cloudy water beneath a thick layer of salt. Beyond the window, the road was frozen in that bleak, bone-chilling winter grey. Yet inside her flat, the glass was clear: no misting, no trails of water running down it. Meanwhile, my own windows were streaming with condensation.

We were having tea when she spotted my confused expression and laughed. “It’s my winter version of the aluminum foil trick,” she said, gesturing towards the bowl. “Summer, foil. Winter, salt water.” It sounded like the sort of grandmotherly tip you read once and promptly forget. But over the following days, I kept thinking about it. How could something so basic appear to work so effectively?

Why winter windows sweat – and where a bowl of salt fits in

On frosty mornings, windows put on a small display of everything happening indoors. Warm air carries invisible moisture from showers, cooking and even breathing, then meets ice-cold glass. Fine droplets form, merge together and quietly trickle down the pane like persistent little snails. The frame grows darker, paint begins to swell, and a patch of mould starts its slow advance in a corner.

That moisture is not entering from outdoors. It is humidity already inside your home, with nowhere else to escape. During summer, some people stick aluminium foil to their windows to keep out sunlight and heat. In winter, the problem is less obvious: moisture trapped indoors and settling on cold surfaces. The window becomes the home’s vulnerable point. That is where a bowl of salty water makes its unassuming entrance.

Imagine a compact city flat with radiators hissing and washing drying on a rack beside the window. A young couple sit at the kitchen table to work, laptop leads winding between coffee mugs. By 9 am, the windows are so misted that they can hardly make out the street. They open a window for “just five minutes”, but the room quickly becomes freezing, so they shut it again.

They turn to the familiar solutions: kitchen roll, an old towel and a daily wipe of the glass. By the third week, the silicone seal along the bottom of the window begins to blacken. Then a friend sends them a picture: a bowl, a handful of coarse salt and some water. “Try this near the window,” she writes. They laugh at the idea: a supermarket science experiment. Nevertheless, they place one bowl on each windowsill.

There is no dramatic result on the first day. No instant transformation. By the fourth morning, though, there is a change. The glass still mists slightly around the edges, but the large streams of water have disappeared. The towel they once used every day remains dry. Looking more closely, they find that the salt in the bowl has developed a crust, rather like frozen snow. Visitors would never notice this small difference, but to the couple it feels like taking back control of their home.

There is nothing magical about the bowl. It is simply physics and chemistry quietly at work. Salt is drawn to water. In technical terms, salt is hygroscopic: it attracts moisture from the air and “absorbs” it into the solution. Put salted water beside a cold window and that small pool of brine acts as a magnet for some of the moisture in the surrounding air.

The glass therefore has less moisture available to collect. Rather than every bit of water vapour settling on the cold pane, some is captured by the bowl instead. It will not alter the conditions throughout an entire house, but on an ordinary windowsill beside a cold wall, it creates a slightly drier micro-zone. Gradually, this can lessen condensation on that particular window. Think of it as a small, inexpensive dehumidifier placed precisely where it is needed.

How to use salty water by the window in winter – the simple method

The process itself is strangely soothing. Choose a bowl that you do not mind becoming slightly marked over time. Half-fill it with tap water, then add a generous handful of coarse salt. Give it one or two stirs. Some of the salt should dissolve, while some should remain visible at the bottom. The water should look slightly cloudy, much like seawater in a shallow rock pool.

Set the bowl on the windowsill, as near to the glass as possible without creating a risk of spilling it onto the frame. One medium-sized bowl per window will normally do for a small room. For a large bay window, use two smaller bowls, placing one at either end. Inspect the bowl roughly once a week: if all the salt has dissolved into the water or it has made a solid crust, replace the mixture. Pour away the liquid, quickly rinse the bowl and prepare a fresh batch.

A few common pitfalls lead people to decide that “this trick doesn’t work”, when their own set-up is actually undermining it. The first is placing the bowl behind heavy curtains or blinds. The salty water needs exposure to the room’s air to interact with it. If fabric covers it, its effect is greatly reduced.

The second mistake is hoping for a miracle in a home that is already saturated with moisture. If you dry three loads of washing in a tiny, unventilated living room, even ten bowls of salt will not rescue the windows. Small everyday measures are still necessary: briefly air rooms, use the extractor fan while cooking and avoid pressing furniture tightly against cold walls. Let’s be honest: nobody truly does all of that every day. But doing it a little more often, alongside the bowls, can help tip the balance.

Another regular error is overlooking the fact that salt has a limit. When the solution is saturated and the salt can no longer absorb additional moisture, the bowl stops doing anything. This is when people say, “It worked at first, then nothing.” The answer is unexciting but straightforward: renew the mixture regularly, particularly in damp spaces such as bathrooms and very small kitchens.

“It’s not witchcraft,” laughs Claire, a 39-year-old tenant in a drafty old building. “It’s just the only low-cost thing that stopped my bedroom window from crying every single morning.”

Her experience is echoed by many others. Forums and social media are filled with pictures of bowls on windowsills, above radiators and in corners where mould had begun to take hold. Some people strongly recommend combining salty water with the well-known summer approach: aluminium foil on the glass or exterior shutters in July to reflect heat, followed by bowls in January to control humidity. The connection is straightforward: in both seasons, the aim is to protect the delicate boundary between indoors and outdoors.

• Use coarse salt instead of fine table salt, as it lasts longer and dissolves more gradually.
• Put bowls by the coldest, most heavily misted windows first, rather than scattering them throughout the home.
• Check for mould on window frames and walls, removing it early before it can spread.
• Combine the bowl method with short daily periods of ventilation rather than depending on it alone.
• Keep pets and young children away from the bowls, as salty water is not suitable for curious tongues.

From small hacks to a different way of living with winter

There is something quietly comforting about these simple, homemade solutions. A bowl of salted water on a windowsill does not announce itself as a “smart home” or “connected device”. It simply sits there, modestly performing a task that goes unnoticed until it no longer does it. During a season of short days and high energy prices, that modest assistance brings its own kind of psychological warmth.

Most of us know the feeling of a home seeming slightly hostile: windows dripping, radiators humming and the air feeling heavy after a shower. Such small measures will not turn an ageing flat into a flawlessly insulated refuge, but they can alter how the space feels day to day. A pane that is a little drier. A frame that stays cleaner for longer. The quiet relief of less wiping, less scrubbing and less concern about the next patch of mould.

Some readers will try the bowl and never stop using it. For others, it may be a modest extra alongside more substantial measures: insulating windows, inspecting vents or using a proper dehumidifier in the dampest room. The underlying principle remains the same as the one that makes aluminium foil helpful in summer and salt water useful in winter: you do not have to accept the season exactly as it arrives. You can adjust your home’s microclimate one bowl at a time, and perhaps pass on the idea to the next person wondering why your windows have stopped “crying”.