An electrochemical reactor to produce oxyhydrogen gas from water based on water electrolysis, comprising a watertight container defined by four perimeter walls (2a, 2b, 2c and 2d), a wall at the bottom and an open top side forming a prismatic cube that holds an electrolytic solution; wherein at least two opposing perimeter walls (2a-2d) and the bottom wall include on their internal face a plurality of equidistant grooves where electrochemical plates are introduced in, being those electrochemical plates placed in parallel and separated one each other to allow the contact with the electrolytic solution; wherein alternating electrochemical plates are fixed at both ends of the top edge to a couple of rods for electrical connections fed by a supple source of electrical power; further comprising: - fastening means in the upper part of the opposing perimeter walls (2a-2d) for holding and fixing an upper cover, and comprising a neoprene gasket on the perimeter for a hermetic sealing; - a plurality of connectors for the supply and discharge of the gas produced in the reactor, where those connectors protrude from the outer part of the group of electrochemical plates through the upper cover; - level sensor elements, temperature sensors, and pressure sensors that are monitored and controlled by an electronic system which is also used to program the operational settings and to store the data collected; - one gas outlet duct connected to at least one of the drilled holes placed in the opposing perimeter walls (2a-2d) of the container; and characterized in that: - the electrochemical plates include a central groove in "V" form at the top edge to allow the effect of communicating vessels in the filling operation; - the upper cover includes, in its lower face, a triangular projection that defines a "V" form with a cylindrical body in the vertex; and - wherein said triangular projection is placed in the area defined by the central grooves at the top edge of said electrochemical plates isolating the inner part of the container when positioning the upper cover. - fastening means in the upper part of the opposing perimeter walls (2a-2d) for holding and fixing an upper cover, and comprising a neoprene gasket on the perimeter for a hermetic sealing; - a plurality of connectors for the supply and discharge of the gas produced in the reactor, where those connectors protrude from the outer part of the group of electrochemical plates through the upper cover; - level sensor elements, temperature sensors, and pressure sensors that are monitored and controlled by an electronic system which is also used to program the operational settings and to store the data collected; - one gas outlet duct connected to at least one of the drilled holes placed in the opposing perimeter walls (2a-2d) of the container; - the electrochemical plates include a central groove in "V" form at the top edge to allow the effect of communicating vessels in the filling operation; - the upper cover includes, in its lower face, a triangular projection that defines a "V" form with a cylindrical body in the vertex; and - wherein said triangular projection is placed in the area defined by the central grooves at the top edge of said electrochemical plates isolating the inner part of the container when positioning the upper cover.