Water softening is the removal of calcium, magnesium, and certain other metal cations in hard water. The resulting soft water requires less soap for the same cleaning effort, as soap is not wasted bonding with calcium ions. Soft water also extends the lifetime of plumbing by reducing or eliminating scale build-up in pipes and fittings. Water softening is usually achieved using lime softening or ion-exchange resins, but is increasingly being accomplished using nanofiltration or reverse osmosis membranes.
Limescale buildup in a PVC pipe
Ion exchange resins, in the form of beads, are a functional component of domestic water softening units
Hard water is water that has a high mineral content. Hard water is formed when water percolates through deposits of limestone, chalk or gypsum, which are largely made up of calcium and magnesium carbonates, bicarbonates and sulfates.
A bathtub faucet with built-up calcification from hard water in Southern Arizona.
A portion of the ancient Roman Eifel Aqueduct in Germany. After being in service for about 180 years, the aqueduct had mineral deposits of up to 20 cm (8 in) thick along the walls.