Improved precision in the H2-H2O equilibration method for ??D analysis has been achieved in an automated system. Reduction in 1-?? standard deviation of a single mass-spectrometer analysis to 1.3??? is achieved by (1) bonding catalyst to glass rods and assigning use to specific equilibration chambers to monitor performance of catalyst, (2) improving the apparatus design, and (3) reducing the H3+ contribution of the mass-spectrometer ion source. For replicate analysis of a water sample, the standard deviation improved to 0.8???. H2S-bearing samples and samples as small as 0.1 mL can be analyzed routinely with this method.