A substance added to detergents to increase their cleansing action, primarily by removing the water hardness cations (magnesium and calcium), which would otherwise e.g. interfere with the action of some types of surfactant. Common builders are sodium triphosphate (which removes the hardness ions by complexation) various types of zeolite (insoluble materials that remove the hardness ions by an ion-exchange effect), and sodium carbonate (soda ash), which precipitates the hardness ions as carbonates.