Drinking water treatment. Pellet reactors being used to soften drinking water. Water softening is the process of removing dissolved calcium ions and other mineral ions. This avoids problems with limescale formation in domestic appliances and pipes, and soap scum in water that is used for washing. A pellet reactor uses pellets (here, fine grains of sand) as a nucleus on which the calcium carbonate and other minerals can form. Sodium ions are used to replace the calcium ions. Water is injected in the base of the reactor and softened water flows from the top. Photographed in France.