Problems with water softeners using salt to soften the water have led to the need for alternatives. A no salt water softener may use magnets to pull minerals from the water, or may use a system to chemically change the minerals. The beauty of these systems is the descaling they do to pipes, tankless water heaters, conventional water heaters, and other water-related appliances in the house. After about 90 days, the water from a saltless water softener has descaled the pipes and fittings, and they will remain clean as long as the softener is operating.
One type of saltless water softener is based on the FREIJE water treatment technology, where electronic frequencies pass through a pipe and create molecular agitation in the water, according to Faraday's Law. This process physically changes the shape and charge of the minerals, which prevents scale build-up.
Some consider a conventional water softener to be saltless, when the water softener salt pellets are replaced by potassium chloride. Technically, potassium chloride is also a salt, but since it's needed for healthy function of the heart, muscles and other physiological processes, its presence in drinking water is not considered to be detrimental. Many people, adults and children alike, have to reduce their intake of sodium for health reasons. Still, this approach is not technically saltless.
There is also a saltless water softener device that operates through the use of magnets, and doesn't require electricity, salt, or maintenance. Unwanted minerals dissolved in the water are reduced to "sub-micron suspended solids" that are swept through the plumbing system before the resulting scaling or interference with detergents.
The German Technical and Scientific Association for Gas and Water has provided a way of testing scale prevention in water systems. To be acceptable by their standards, a water softening system must be 80% effective. In the US, there is one saltless water softener system that meets that criteria. To be sure about the softener system you buy, be sure to check the DVGW W512 score for effectiveness.