Using DFT calculations, we have considered different adsorption configurations of water molecules on MgO surfaces. In some cases, we have observed a chemical reaction between water and the surface, with the formation of hydroxyl groups. We have systematically compared the calculated Raman spectra of the final optimized structures with the measured spectra from MgO nanoparticles. Our results confirm the high reactivity of MgO surfaces with water. Some obtained structures can be considered precursors for the transformation of MgO into Mg(OH)2. We suggest that some of them could be identified using Raman spectroscopy. Our study confirms the high potentiality of Raman spectroscopy, associated with numerical calculations, for the study of chemical reactivity of nanoparticles