Electrodeionization is a water treatment technology that utilizes electricity, ion exchange membranes and resin to deionize water and separate dissolved ions (impurities) from water. It differs from other water purification technologies in that it is done without the use of chemical treatments and is usually a polishing treatment to reverse osmosis (RO). 

The EDI process produces industrial process water of very high purity. When fed with low TDS feed (e.g., feed purified by RO), the product can reach very high purity levels (e.g., 18 Megohms/cm[2]). The ion exchange resins act to retain the ions, allowing these to be transported across the ion exchange membranes. The main applications of EDI technology, such as that supplied by Ionpure, E-cell and SnowPure, are in electronics, pharmaceuticals and power generation.