NOVELTY - The conversion reactor comprises, in a single enclosure, a catalytic zone for conversion of carbon monoxide with water, a water tank, and vertical tubes (20) filled with the catalysts. The catalytic zone disposes an inlet pathway for gas flow and an outlet pathway for the converted flow, and comprises catalysts for carbon monoxide into water. The water tank is disposed in the inlet and outlet pathways, and comprises a reservoir whose volume is 0.5-20 times the volume of the catalyst in the form of liquid and/or solid. The catalytic zone and water tank are in thermal contact with each other.    USE - The reactor for conversion of carbon monoxide into water is useful in an installation for the production of hydrogen (claimed), which is useful as a source for a fuel cell used in under water vehicles and space vehicles for mining.    ADVANTAGE - The conversion reactor is simple and compact thus ensuring energy efficient conversion of carbon monoxide into water without clogging and easy production of hydrogen without formation of precursors, pre-combustion of the hydrocarbon charge and risk of condensation of the synthesis gas.    DETAILED DESCRIPTION - The conversion reactor comprises, in a single enclosure, a catalytic zone for conversion of carbon monoxide with water, a water tank, and vertical tubes (20) filled with the catalysts. The catalytic zone disposes an inlet pathway for gas flow and an outlet pathway for the converted flow, and comprises catalysts for carbon monoxide into water. The water tank is disposed in the inlet and outlet pathways, and comprises a reservoir whose volume is 0.5-20 times the volume of the catalyst in the form of liquid and/or solid. The catalytic zone and water tank are in thermal contact with each other. The water tank comprises plates defining two insulated spaces. The catalytic zone of the reactor comprises spaces in which the catalysts are prepared, and the water tank of the reactor comprises vacuum spaces. An INDEPENDENT CLAIM is included for a process for conversion of carbon monoxide into water.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a reactor for conversion of carbon monoxide into water.    Gas effluent supply pipe (1)    Final product outlet pipe (12)    Fluid (13)    Vapor product outlet pipe (14)    Vertical tubes. (20)