It's best to store hydrated clay or liquid clay in an opaque, ceramic, stoneware crock, glass or PET plastic air tight, non-metallic container.

Keep hydrated or liquid clay out of direct sunlight and at cool room temperature.  It maybe refrigerated or not depending on your preference.

One other thing to consider when storing hydrated clay is that it's important not to 'double dip' when scooping some hydrated clay out of your storage container. This just means using a clean utensil every time you remove some of the hydrated clay, and not putting your fingers or spoon (use plastic, wooden or rubber) back into the clay for another dip after you've already put that spoon into your mouth. It just makes sense to do what you can to keep the hydrated clay as pristine as possible in order to prevent it from being contaminated in any way.

Dry powder clay is easily stored in most places but keep it out of close proximity to gasoline, chemicals, pesticides and herbicides or anything with a strong odor.  Always keep the lid on tight on any clay products. Powdered clay stored properly will keep indefinitely.

Hydrated and liquid clays stored properly will last for years.  A good indicator that your clay has gone bad it to smell it before using.  If it has a sour, perfume, or musty odor you know it has been compromised and it is not advisable to use in this condition. Hydrated clay has a tendency to get thicker the longer it is kept.

Treat your clay with common sense and respect and it will stay fresh and usable for a long time.