Micro-traces of water in gases have been determined by using a combination of a conversion reactor column and a high sensitivity hydrogen gas sensor (abbreviated here to CRHS-GC). A special purge installation was designed to clean the system with dried and purified liquid nitrogen. Micro-traces of water in gases first were introduced into the reactor column. The column was prepared by filling with a mixture of lithium and aluminium hydride (LiAlH 4 ) and glass fibre in a vacuum box, where the water present reacted with LiAlH 4 at about 60 • C. Hydrogen was released and determined by the hydrogen gas sensor, which was calibrated by a series of standard micro-trace hydrogen mixture gases. The experimental results showed that this method can be used to determine micro-traces of water in gases quickly, accurately and at a low cost. Only about 2-5 litres of sample were needed during each analysis. The method developed does not have the shortcoming of direct determination of micro-traces of water in gases that is caused by the absence of appropriate traceable calibration gases.