Demineralization Systems (Deionization Systems) are another treatment used in water purification. In demineralization systems, synthetic resins can take anions and cations in water instead of filters. Generally, Anionic Resins and Cationic Resins are kept in separate columns, but Mixbed systems where these resins are in the same columns are also frequently used. Resins regenerated by using acid and caustic can become ready for use again.