And I don't mean stain removers, but literally tap water.

See here's the thing, you can't remove a stain without some sort of friction, and water reduces friction. Yet if I say, spill some coffee and later remove the coffee stain, if I were to wipe it with a cloth, very little happens. If I wet the cloth, it's stupidly easier.

  • 2
    $\begingroup$ Perhaps it has something to do with the stain being dry. Adding water dissolves the stain, and then the cloth is able to absorb the water now containing the stain molecules. $\endgroup$
    – Tweej
    May 9, 2016 at 15:23
  • 3
    $\begingroup$ I think this is better suited to the Chemistry boards. $\endgroup$ May 9, 2016 at 15:29

1 Answer 1


As @Tweej suggests, it's because of water solubility. Because water molecules are quite polar, most things that are charged or polar are soluble in it (i.e.~"hydrophilic"). When a coffee stain dries up, the residue sticks to the surface. But when water is applied, it will readily mix with the water, and more easily be removed.

Fats and oils are hydrophobic, and tend to separate from water --- which is why oil stains are so much harder to remove (with water, and water-based cleaners).


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