To describe reactions occurring at the solid/water interface is currently one of the major challenges in modeling in Heterogeneous Catalysis in particular in the context of Green Chemistry and biomass valorization where water is a natural solvent. Modeling such an interface requires a proper depiction of the water solvent together with an adequate description of the surface state. Several approaches are available nowadays in the literature, from continuum models to a full explicit description of the liquid water.[1] We have recently shown that continuum models are key to a proper description of reactions occurring at the electrochemical interface on the formic acid oxidation into CO2.[2] They also open the door to a proper inclusion of the effect of co-adsorbed anions in thermal heterogeneous catalysis.[3] In both cases, charges are involved and the electrostatic contribution in the major one. When H-bonding between the liquid water and the reactant or intermediate is crucial, continuum models are not sufficient and an explicit inclusion of water molecule is a necessity. As a first step, micro-solvation can be an effective approach that allowed us to interpret solvent effect in the conversion of levulinic acid into γ-valerolactone.[4] Moving to a full description of reactivity the water/metal interface is still beyond a full complete DFT approach provided the minimal size of the periodic cell that is necessary and the minimal sampling required. Nevertheless, being less demanding, inspecting transformations occurring at oxide/water interface is now reachable, as illustrated by our recent work on the stability of γ-alumina in water.[5] REFERENCES [1].M. Saleheen, A. Heyden, ACS Catal. 2018, 8,. 2188-2194 [2].S. N. Steinmann, C. Michel, R. Schwiedernoch, J.-S. Filhol, P. Sautet, Chemphyschem, 2015, 16, 2307-2311 [3].P. Wang, S. N. Steinmann, G. Fu, C. Michel, and P. Sautet, ACS Catalysis, 2017, 7, 1955–1959 [4].C. Michel, J. Zaffran, A. M. Ruppert, J. Matras-Michalska, M. Jedrzejczyk, J. Grams, P. Sautet, Chem. Comm. 2014, 50, 12450–12453 [5].R. Réocreux, “Biomass derivatives in heterogeneous catalysis: adsorption, reactivity and support from first principles”, PhD thesis, (2017)