I had some fleas issues so I read about putting salt and sodium bicarbonate in the carpet and in the edges with the purpose to reduce the humidity and dehydrate eggs and larvae. After few days, the weather changed, to humid, rainy and foggy. UK weather... Suddenly, out of nowhere I found all the floors and carpets humid and specially in areas where the mixture was more abundant, there were quite a lot of drops of water. I wonder why. Probably the hygroscopic property of salt and sodium bicarbonate, in a change in humidity or atmospheric pressure released the water accumulated during several days. I have no idea.
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$\begingroup$ After the salt and the sodium bicarbonate absorb the water, where else do you think should the water go to? $\endgroup$– DHMOSep 5, 2016 at 20:06
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I've never heard of sodium chloride/sodium bicarbonate being an effective dessicant. Pure sodium chloride is not hygroscopic at all.
However, in air sodium bicarbonate slowly decomposes to sodium carbonate which in fact is hygroscopic. If sodium carbonate, and hygroscopic impurities in table salt, such as magnesium chloride or calcium chloride, deliquesce in air of high humidity to give small droplets then these droplets start to grow due to a high concentration of dissolved salts (including sodium chloride and bicarbonate). The effect is reversible at low humidity or higher temperature.
