A plain glass, some coarse salt, a corner of the bathroom shelf. The trick is spreading from Europe to American homes, and it’s popular for good reason: it costs almost nothing and looks harmless. But what does a glass of salt in the bathroom really do? Here’s what it’s for, why so many people do it, and where its limits are.
Why salt?
Salt is hygroscopic: it attracts water molecules from the air. Left in an open glass in a small, humid room, coarse salt slowly picks up moisture, clumps together and eventually looks damp. That’s the whole principle, and it’s the same idea behind commercial moisture absorbers, which use a far more powerful salt, calcium chloride.
What it’s for
- Catching a little moisture in a small bathroom without a window, a powder room or a cabinet under the sink.
- Showing you there’s a humidity problem: if the salt is soaked and hard within days, the room is too damp.
- A simple scent diffuser: many people add a few drops of essential oil, such as eucalyptus or lavender, for a light fragrance.
- Zero cost and zero electricity: you already have the salt in the kitchen.
It’s also popular in closets, gym bags and cabinets under the sink, where a little damp air gets trapped and a musty smell settles in over time.
How to do it
- Fill a glass or small jar two-thirds with coarse salt, such as rock salt or kosher salt.
- Place it on a shelf, away from the shower spray and out of reach of children and pets.
- Stir it once a week. When it’s hard and damp, replace it.
Be realistic about the effect
Even the dedicated products are slow. In a test by the consumer group CHOICE, a calcium chloride absorber removed about 2 ml of water per hour at 65% humidity, while the dehumidifiers tested removed between 113 and 388 ml per hour. A glass of kitchen salt absorbs even less. It can help in a small closed space, but it won’t dry a bathroom after a hot shower.
What really keeps a bathroom healthy:
- Run the exhaust fan during your shower and for about 20 minutes after.
- Crack the door or window open when you’re done.
- Wipe down the shower walls and hang towels to dry outside the bathroom if possible.
- Aim for indoor humidity below 60%, ideally between 30 and 50%, as the EPA recommends.
The limit
A glass of salt does not remove mold, and it doesn’t purify the air. If you see black spots in the grout, a musty smell that won’t go away or peeling paint, the problem is ventilation or a leak, and salt won’t fix it.
Moisture is a winter enemy outside the house too, as we explained with the white pebbles that trap moisture against your walls. And for a scent that lasts, some people prefer orange peels simmered with cinnamon or three bay leaves under the mattress.
A glass, some coarse salt and a fan that runs a little longer. That’s the trick.
