Activated carbon-based capacitive deionization (CDI) electrodes have been coated with gold nanoparticles through a facile impregnation method. Activated carbon (AC) in the original and nitric acid treated form had been used. Au addition, irrespective of AC being acid treated or not, increases the salt adsorption capacity (SAC), increases charge efficiency and reduces specific energy consumption (SEC) in the CDI process. While applying both acid treatment and gold deposition result in maximum SAC (6.1 mg g−1), sole gold decoration is accompanied with least SEC (0.7 KWh (kg adsorbed ion)−1). Interestingly, gold addition significantly reduces cathodic reduction and anodic oxidation reactions in the case of untreated and treated AC, respectively. A theoretical explanation has been proposed.