Rock salt, solar salt or evaporated salt are the primary salts used in water softeners and are all primarily sodium chloride (NaCl). Water softeners exchange insoluble minerals, including calcium and magnesium, for a more soluble mineral: sodium chloride. Removing these minerals makes the water more effective at dissolving soaps and detergents. The process reduces the buildup of minerals in pipes.
Evaporated salt is the purest form of sodium chloride based salts that can be used for softening water. This type of salt is dissolved from its raw state and then converted back into sodium chloride by extracting all the moisture using heat. What is left is 99 % pure salt that is very effective in treating hard water.