Softeners are devices that use ion exchange resin, an insoluble matrix, to clean and deionize water. The resin contains pores with highly developed surfaces that attract ions and release them. The ion exchange resin is manufactured to prefer one ion over another, and most are made from cross-linked polystyrene. In addition, the regeneration process involves using water that is disposed of as waste. Another type of softener treatment plant is ionized water. These units use negative ions to reduce dissolved contaminants in water.