Rock salt, solar salt or evaporated salt are the primary salts used in water softeners and are all primarily sodium chloride. Solar salt, made by evaporating seawater, has the lowest sodium chloride levels at 85 percent. Evaporated salt, from water sources in the earth, is 99.9 percent sodium chloride.
Rock salt contains more insoluble impurities than the other two types of salt. These impurities increase the frequency of cleaning the water softener. Evaporated salt makes the best choice in systems that require the greatest amount of salt. Solar salt includes a slightly higher percentage of insoluble materials.
Water softeners exchange insoluble minerals, including calcium and magnesium, for more soluble sodium. Removing these minerals makes the water more effective at dissolving soaps and detergents. The process reduces the buildup of minerals in pipes.