Water softening is the removal of calcium, magnesium, and certain other metal cations in hard water. The resulting soft water is more compatible with soap and extends the lifetime of plumbing. Water softening is usually achieved using lime softening or ion-exchange resins.
Water softening methods.
Practical means for softening water rely on ion-exchange polymers or reverse osmosis. Other approaches include precipitation methods and sequestration by the addition of chelating agents. Devices that claim to use magnetism or electricity as a "water softening" technique are fraudulent and often utilize pseudoscience.