The catalyzed exchange reaction between liquid water and hydrogen gas has been studied using a hydrophobic catalyst of platinum deposited on a porous Teflon support. The reaction was studied with a new method in which a mixture of water mists and hydrogen gas moves downward through the catalyst bed co-currently. This new method was employed to improve the poor contact efficiency between liquid water and hydrogen gas in the hydrophobic catalyst bed. It was found that the reaction rate increased an order of magnitude over the conventional method in which liquid water and hydrogen gas react countercurrently. These experimental results have been analyzed in terms of a rate determining step and compared with previous ones.