Hard water has dissolved limestone in it. Limestone is mostly calcium carbonate. Calcium carbonate is everywhere, and of which, teeth, bones, seashells, pearls, mother of pearl. Stalactites and stalagmites, the “White Cliffs of Dover”, marble and the “Carlsbad Caverns”, for example, are made. When hard water is heated, it causes scale to form inside pipes, causing constriction. Hard water reacts with soap causing soap scum, the stuff of which bathtub rings are made. It coats your skin, your hair, your appliances, your dishes and flatware. It can cause dry skin, rashes and acne. Correction is recommended for any reading over 3.5 grains per gallon, and pays for itself in cost savings.