The Norton Water Stones need to be completely submersed in water for 15 min before using. So when you are done using them obviously they have a good deal of water still in them, right? The blue boxes that they come in have holes in them, but I am concerned that if I put them back in the boxes right after using them that they will mildew, and I typically let them set out on the counter for a number of days before putting them away. Is this necessary? If so for how long?