Here we discuss the importance of water in proton solvation for the hydrogen evolution on polycrystalline gold microelectrodes. We perform cyclic voltammetry in acetonitrile electrolyte, in presence and absence of added amounts of water, with the interfacial movement of water and ions monitored by means of in situ Fourier Transform InfraRed (FTIR) spectroscopy. Our results show that trace amounts of water accumulate at the gold-acetonitrile interface. In the absence of protons (from a proton source), this water leaves the interface with more negative potential. In the presence of protons, we observe preferential solvation of protons by water, and water accumulates at the electrode surface under conditions of hydrogen evolution. Tafel plot analysis shows that the hydrogen evolution on gold in acetonitrile presents the same rate-determining step as for polycrystalline platinum, implying that the first electron transfer to yield adsorbed hydrogen is the rate-determining step of the reaction. (C) 2016 Elsevier B.V. All rights reserved.