The hardness of water depends on the density of calcium and magnesium salts contained in it. Water is considered hard if the amount of minerals is over 150mg per liter of water; middle hard water is 70~150mg, and under 75mg is considered soft. Slightly harder water contains natural calcium and magnesium. The activated calcium and magnesium in ionized water have been shown to be are beneficial to general health. In the right amounts, these ions give the cells of our blood vessels special protection.