Ion exchange resins consists of two main types, i.e., cation exchange resins, that exchange positively charged ions, such as sodium, for calcium, and anion exchange resins, that exchange negatively charged ions, such as chloride, for arsenic. Resins are usually made from the polystyrene polymer backbone and differ only by their specific functional groups. The ion exchange systems are usually regenerated with sodium chloride. The strength of the solution depends on the strength of the adsorption bond. Usually, 0.1 N NaCl is effective in removing even strongly adsorbed anions.