The concentration polarization in electrodeionization is easily obtained with NaCl, Na2SO4, and KCl; above a critical voltage, we observe water dissociation and a neat decrease in efficiency, which constitute limiting parameters. These phenomena are not observed with amphoteric salts such as NH4CH3COO. The efficiency increases continuously with the applied voltage without any apparent water dissociation or other abnormal phenomena. The H3O+ and OH- issued from the polarization water dissociation are immediately and simultaneously neutralized by NH4+ and CH3COO-. The problem of polarization in EDI may be then easily solved by the addition of "sacrificial" amphoteric salts, which improve seriously the efficiency.