It is inorganic (does not decay). I leave mine out of the refrigerator for convenience. I'm on my 58th day of over 100 degree temp; so sometimes I put it in the refrigerator just to have a cold drink. However, I hate to keep opening the door. Ice cubes work.
You only need to make sure that your water is not contaminated by something organic; such as lemon juice or something you think will enhance it. Instead, add those to your glass of the DE water, if you really want to.