A porous carbon foam electrode (CF) modified with reduced graphene oxide-Ag (rGO-Ag) nanocomposite has been fabricated to purify water. It can perform as an antibacterial device by killing pathogenic microbes with the aid of a 1.5 V battery with very little power consumption. The device is recycled for ten times with good performance for long term usage. In other words, the device may be implemented as fast water purifier to deactivate the pathogens in drinking water.