Hard water is water that contains invisible dissolved rock, principally calcium and magnesium minerals. Most commonly, people notice the effect of hard water because of a build-up of scale in kettles and on shower heads, or other domestic appliances that use water. The problems associated with hard water can be resolved by installing a water softener which removes the hardness minerals from the water. Water softeners operate on the ion exchange process. Essentially the water passes through millions of negatively charged tiny resin beads which attract the hardness minerals – calcium and magnesium. The resin is then washed to remove the minerals and is used again. And salt is essential for the regeneration of the ion exchange resins.