Arsenic is naturally occurring in many parts of the world. There are two forms of Arsenic in water: arsenite (III) and arsenate (V). Arsenite (III) is neutral in charge while arsenate (V) is negatively charged. Generally, arsenite (III) must be oxidized to arsenate (V) prior to treatment. Arsenic (V) molecule in solution is chemically similar to that of sulphate.

There are several identified methods for removing arsenic from water. Anion exchange is recognized as the best available process which can effectively remove arsenic As (V) at greater than 95% efficiency. Strong base anion exchange resins are usually used for arsenic removal.