The chemical composition and dissociation behaviour of water adsorbed on clean and oxygen pre-covered Pd{111} was studied using high-resolution time-resolved and temperature-programmed X-ray photoelectron spectroscopy. We find that water remains intact at all temperatures up to desorption on the clean surface and at high oxygen coverage(0.69ML) when a surface oxide is formed. The highest desorption peaks occur at 163K from the clean surface and at 172K from the surface oxide. At the intermediate coverage of 0.20ML oxygen reacts with coadsorbed water at 155K, to generate a mixed H 2 O/OH layer exhibiting a (3×3)R30° diffraction pattern, which is stable up to 177K. The measured ratio between intact water and the hydroxyl species in this layer varies between 1.5 and 2 depending on temperature.