A water treatment system comprising: a water treatment unit configured to electrically treat water, wherein the water treatment unit is provided in an intermediate portion of a water passage allowing the water to flow, and the water treatment unit includes a treatment vessel comprising a plurality of discharge units (230a, 230b), each discharge unit (230a, 230b) including a first lane and a second lane, which are separated by an electrically insulating plate-like divider, and through which water flows, a first electrode being in contact with the water of the first lane, a second electrode being in contact with the water of the second lane, and a high-voltage generator connected to the first and second electrodes (231, 232) and applying a predetermined voltage to the first and second electrodes, a discharge member included in each divider made of an electrically insulating material closing a hole of the divider and having a discharge hole with an electrical resistance of several MΩ cut in the center of the discharge member, the discharge hole defining a current path between the first and second electrodes (231, 232), an insulator at an inflow side configured to electrically insulate the water flowing to the water treatment unit, an insulator at an outflow side configured to electrically insulate the water flowing out of the water treatment unit,, wherein the insulator at the outflow side includes a downstream vessel being surrounded by outer walls and by an outlet wall of the treatment vessel, the outlet wall separating the downstream vessel from the treatment vessel and including outlets, the outlets being configured to allow the water to flow out of the first and second lanes (221a, 221b) in form of drops toward the downstream vessel connected to the water passage, a predetermined height being provided between the outlets and a bottom of the downstream vessel or a surface of the water stored in the downstream vessel, characterized in that the insulator at the inflow side includes a nozzle header having a plurality of spray nozzles, each nozzle being associated with one of the lanes (221a, 221b) and configured to spray the water in form of droplets to the associated lane (221a, 221b) of the water treatment unit. a water treatment unit configured to electrically treat water, wherein the water treatment unit is provided in an intermediate portion of a water passage allowing the water to flow, and the water treatment unit includes a treatment vessel comprising a plurality of discharge units (230a, 230b), each discharge unit (230a, 230b) including a first lane and a second lane, which are separated by an electrically insulating plate-like divider, and through which water flows, a first electrode being in contact with the water of the first lane, a second electrode being in contact with the water of the second lane, and a high-voltage generator connected to the first and second electrodes (231, 232) and applying a predetermined voltage to the first and second electrodes, a discharge member included in each divider made of an electrically insulating material closing a hole of the divider and having a discharge hole with an electrical resistance of several MΩ cut in the center of the discharge member, the discharge hole defining a current path between the first and second electrodes (231, 232), an insulator at an inflow side configured to electrically insulate the water flowing to the water treatment unit, an insulator at an outflow side configured to electrically insulate the water flowing out of the water treatment unit,, wherein the insulator at the outflow side includes a downstream vessel being surrounded by outer walls and by an outlet wall of the treatment vessel, the outlet wall separating the downstream vessel from the treatment vessel and including outlets, the outlets being configured to allow the water to flow out of the first and second lanes (221a, 221b) in form of drops toward the downstream vessel connected to the water passage, a predetermined height being provided between the outlets and a bottom of the downstream vessel or a surface of the water stored in the downstream vessel, characterized in that the insulator at the inflow side includes a nozzle header having a plurality of spray nozzles, each nozzle being associated with one of the lanes (221a, 221b) and configured to spray the water in form of droplets to the associated lane (221a, 221b) of the water treatment unit.