A "salt-free" or "water conditioner" is different from a traditional water softener in that it does not use ion exchange to remove hard water minerals. Instead, it uses a process called template-assisted crystallization (TAC) to convert the hard water minerals into harmless, microscopic crystals that cannot adhere to surfaces or cause scale buildup. This process does not actually remove the minerals, but it changes their physical properties so that they do not cause hard water problems.
A traditional water softener uses ion exchange to remove hard water minerals. It exchanges the hard water minerals with sodium ions, which are then carried away in the wastewater. This process does remove the minerals, but it adds sodium to the water supply. In contrast, a "salt-free" or "water conditioner" does not add anything to the water supply, making it a more environmentally friendly option. It's also more suitable for people who are on a low sodium diet.
In summary, a traditional water softener removes the minerals from water by exchanging them with sodium ions, while a salt-free water softener changes the physical properties of the minerals so they do not cause hard water problems.