Rock Salt

• Rock salt is just what the name sounds like, lumps of salt still in rock form. This type of salt is harvested from underground salt mines using mining techniques. Rock salt is completely natural. Rock salt is the least expensive salt for softeners but it contains material that is not water-soluble. This means you must clean out your water softener reservoir more often when using rock salt to prevent clogs and build up from by-products. Rock salt is damaging to some water softening systems due to its high content of undesirable materials.
  
  

Solar Salt

• Solar salt is another natural salt, though this is not retrieved from mines. Solar salt is often harvested from evaporated sea water. This salt is of slightly higher quality than rock salt, containing less of the materials that are not water-soluble. Solar salt is a good option for water softeners treating very hard water, as it contributes less to the regular cleaning maintenance required by water softeners due to salt and hard water. Reservoir clean-out with solar salt is done less frequently than it is when using rock salt.
  
  

Evaporated Salt

• Evaporated salt is the highest quality salt used for water softeners. This type of salt is mined from the same source as rock salt -- an underground mine. However, rather than mining the lumps of salt, evaporated salt is mined from deposits of dissolving salt. Coal or natural gas energy is used to evaporate any moisture left in the salt. This salt contains little to no material that is not water-soluble. This type of salt contains up to 99.9 percent sodium chloride, a component highly desirable in dissolving hard water minerals. This salt reduces the amount of reservoir clean-out you must perform.
  
  

A Word About Pellets and Block Salt

• Both rock and solar salt are available in block and pellet form. These forms are also used in water softeners, though not all softener systems recommend them. The salt blocks and pellets are made by adding an adhesive material to the salt to help them stick to the block or pelleted shape. This adhesive adds even more undesirable material and over prolonged use makes the water softener malfunction. Always read the owner's manual for your system to determine if block or pellet salt is safe for use.