  The initial interaction of water with semiconductors determines the
electronic structure of the solid-liquid interface. The exact nature of this
interaction is, however, often unknown. Here, we study gallium phosphide-based
surfaces exposed to H2O by means of in situ reflection anisotropy spectroscopy.
We show that the introduction of typical imperfections in the form of surface
steps or trace contaminants not only changes the dynamics of the interaction,
but also its qualitative nature. This emphasises the challenges for the
comparability of experiments with (idealised) electronic structure models for
electrochemistry.
