Catalytic hydrogenation of nitrite in drinking water demands control over the selectivity towards nitrogen, minimizing the formation of ammonia. This selectivity is strongly influenced by the H/N ratio of reaction intermediates at the catalyst surface. Therefore, we fabricated a membrane reactor that feeds separately hydrogen gas and a nitrite solution. This allows dosing low but homogeneous hydrogen concentrations along the axial direction of the catalyst bed. As a consequence, low H/N ratios can be achieved, favouring the formation of nitrogen without limiting the nitrite conversion. We demonstrate that this reactor concept offers better nitrogen selectivity than conventional reactor configurations where hydrogen is pre-dissolved in the nitrite solution.