Dewatering is pretty much exactly what you'd think, albeit the word is used for some very different processes. In the WD40 context it's neat when you see it for the first time though. As I remember back in the stone age we'd get a beaker full of the stuff, which is superficially like kerosene, and hang a lump of wet cotton wool in it and time how fast the drops of water were forced out and fell to the bottom in order to test it. PDQ no water in the cotton wool. Always felt kinda magical to me. Probably test it electronically now, far more accurate but less fun to watch!