Get our free book (in Spanish or English) on rainwater now - To Catch the Rain.
Storage life for salt is indefinite. So long as you keep it dry and do not let it get contaminated, it will never go bad. Over time, iodized salt may turn yellow, but this is harmless and may still be used. Salt it rather hygroscopic and will adsorb moisture from the air if not sealed in an air-tight container. If it does adsorb moisture and cakes up, it can be dried in the oven and then broken up with no harm done.
All salt, however, is not the same. Salt comes in a number of different varieties, each with its own purpose. Very little of the salt produced in the United States is intended for use in food. The rest of it, about 98%, has other uses. Therefore, it is important to be certain the salt you have is intended for human consumption. Once you are satisfied it is, you should then determine its appropriateness for the tasks to which you might want to set it to. Below is a partial list of some of the available salts.
Part of the Mormon Basic Four
Trace amounts of the element iodine (about 150 micrograms of iodine per day for adults) are necessary to prevent problems with thyroid function such as goiter (enlargement of the thyroid gland). Dietary iodine is readily available in seafood and sea vegetables ("seaweed", marine algae, commonly used in Japanese cuisine), but is rare in other dietary sources. Therefore trace amounts of iodine are commonly added to dietary salt. It may be worth considering this when stocking salt intended for long-term survival purposes.