Capacitive deionization (CDI) is a promising technology for water purification and desalination. CDI can be widely applied in the many fields, including domestic water purifiers, arsenic-contaminated groundwater remediation, high-tech industrial water purification system, industrial wastewater treatment systems and, water reuse systems. Following the same working principle of electric double-layer supercapacitors, CDI can be operated at a low pressure (0.2~0.3 MPa) and a low voltage (0.8~1.2 V). Therefore, the operation advantages of CDI have low energy input (< 0.5 kWh/m3), high water recovery (70~90%), low fouling potential, no secondary pollution, and environment friendliness. In CDI, ions can be removed from water by imposing an electric field on a pair of highly porous carbon electrodes during the charging step. Herein, the salt removal efficiency can be controlled between 50% to 90% via manipulation of CDI stack, in which the electrodes are connected in series. At the same time, a high water recovery ranging from 70% to 90% can be obtained. After the saturation, the electrodes can be regenerated at short-circuit mode. Note that direct energy recovery can be achieved by incorporating with a supercapacitor. We can recover almost 40% of stored energy from the desalination of brackish water. Note that activated carbons can be considered as the most cost-efficient electrode material for CDI applications. Especially, activated carbon can be derived from biomass recovery resources. Furthermore, CDI show advantages of low environmental impacts and energy demand along with a global warming potential of 1.43 Kg CO2 eq, which is 40% lower than that of reverse osmosis.