[en] A simple new technique for quantitative reduction of water to hydrogen gas for isotopic analysis is described. Individual pyrex glass tubes are used as both reaction vessels (for the reaction of zinc shot with water to give hydrogen), and sample bottles (to transfer hydrogen to the mass spectrometer for analysis). The technique is based on that reported by Coleman et al. (1982), but we have added an additional step, in which the zinc shot and tube is heated to the reaction temperature and the resultant gases are pumped away before the water sample is admitted. Results show good precision and memory effects are almost eliminated