Got one, no longer have to descale the toilets, scrub sink to get rid of limescale etc. Highly recommended provided it’s metered properly i.e. only regerates as required. Also, fix all dripping taps etc or it’ll cost a fortune softening water that you don’t use.
They work by subsituting sodium ions for the calcium ions in your water using an ion exchange resin. The sodium and carbonate ions will then be in your water. You don’t want to be drinking the softened water unless you want a high sodium diet!
The salt regenerates the ion exchange resin by replacing the calcium ions captured from the water with new sodium ions.