Dirt and dust enter the water through the wind or with the swimmers. Small impurities (colloidal particles) cause the water to become cloudy. Clarification of the water can be achieved by using flocculating agents, which are able to bind the dust impurities into clumps that are already trapped by the sand filter or settle on the bottom of the pool. The sediments are sucked out of the bottom of the pool with a vacuum cleaner. In this way, the consumption of disinfectants can be considerably reduced and the water can be kept perfectly clear.