Alpha, there's basically 2 ways of doing it. The first one is to just add distilled or freshly boiled water directly to the snuff and mix it in. The second option is to put the tin of snuff into a Tupperware container and put a small container of water in with it and put the lid on and set it someplace warm or warm and sunny so that the water evaporates. The snuff will suck up the moisture quite readily. Its also a good way to scent a snuff with vanilla, or an alcohol like rum or whiskey.
Hope this helps