We report on the application of the Car-Parrinello mol. dynamics method (CPMD) to the interaction of water ensembles with Pd(100) model surfaces.Periodic Pd50O8 and Pd18O2 slabs covered with nine and 18 water mols., resp., were employed to analyze the balance of adsorbate-adsorbate and adsorbate-surface interactions as a function of water ensemble size, in the limiting cases of a clean surface and high surface coverage with at. oxygen.Our simulations suggest that 'liquid' water mols. are distributed, for the most part, randomly on Pd(100) at 300 K, with a characteristic intermol. distance distribution in distinct regions of the water/metal interface.The structure of low-mobility local water clusters which stay close to the surface resembles that of earlier proposals based on thin film experimentsIn addition, our results corroborate the exptl. finding that a high surface coverage with oxygen reduces the water-Pd interaction compared to that on the clean solid.