There are generally three different types of water softener salts available:
Some retailers sell technologies meant to prevent scale build–up in household appliances without the use of salt, and sometimes even water. Most of these alternative technologies do not soften water (i.e. do not remove calcium and magnesium) but instead change the properties of suspended solids in the water to stop scale from forming on water heater elements, taps, etc. In some cases the technologies still require backwashing. Examples of these water softener alternatives are:
There is currently very little information published by independent agencies to verify the effectiveness of these new technologies. A recent study published by the U.S. Water Reuse Research Foundation clarifies the effectiveness of the four technologies listed above.