Ion Exchange is a water treatment process in which unwanted dissolved ions in water (calcium, iron, arsenic, nitrates etc.) are swapped with more desirable ions from the resin. Typically used as a means of softening or demineralizing water, ion exchange is particularly well suited as a treatment strategy when trying to remove a specific low concentration pollutant, for example, arsenic from well water. Ion exchange resins are split up into two functional groups, cation (positively-charged) and anion (negatively-charged,) and these functional groups attract ions of an opposing charge. Mixed-bed resins are a combination of the two functional groups and are used either as a final polishing stage to remove any residual ions or in small-scale applications. Resins are either single use, or able to be "recharged" through a chemical process called regeneration.