An H2-water equilibration method using a novel re-usable Pt catalyst has been developed for hydrogen isotope analysis of natural waters. The reproducibility is ±0.8‰, which is comparable with the conventional water reduction methods by U or Zn metal. Equilibration times of 1 and 2 hr. were sufficient for the analysis of a freshwater and Dead Sea brine sample, respectively. This method gives hydrogen isotope activity ratios of natural brines, which have not been analyzed routinely before. This method is applicable to the automated multisample analysis of hydrogen isotopes.