There are various kinds of water softener salt that you could purchase. The 3 most often used types are evaporated, stone and solar salts. The way the system performs is dependent on the kind that you use. There is not one that's generally advocated over another for general use. The variables in your scenario will come in to play, like the kind of unit you have, the hardness of the water and the availability in the region. Evaporated salts are a number of the purest grades available. They're usually crystallized and purified from brine. This will be done in a production plant comparable to the kind that processes table salts.