A water-activated cell comprises an acidic medium including an acidic substance and having a first electrode disposed therein, a basic medium including a basic substance and having a second electrode disposed therein, which basic medium is disposed adjacent to or near the acidic medium, a first reaction substance including a first active material that causes an oxidation reaction at the first electrode, a second reaction substance including a second active material that causes a reduction reaction at the second electrode, and a water-injecting device for injecting water or an aqueous solution into an area where the acidic medium, the basic medium, the first reaction substance, and the second reaction substance exist together, so as to initiate a discharging reaction by the acidic substance, the basic substance, the first active material, and the second active material.