In presence of a solution with finite salt concentration, ions adsorb at the solid wall. We define the average number of ions adsorbed at the solid walls, N Ads , based on a distance criterion: When the distance between an ion and the solid becomes similar to the lattice spacing we consider it adsorbed. We checked that different definitions of the adsorbed amount do not alter our conclusions. For both NaCl and Na 2 SO 4 surfaces, there are more Na + ions adsorbing than Cl -and SO 2- 4 ions, respectively (Fig. ). As a consequence, both solid surfaces acquire a net positive surface charge, a phenomenon that has been previously reported both experimentally and numerically for NaCl surfaces. In addition, the atomic roughness of both surfaces is modified due to the presence of adsorbed ions. Ions were observed to adsorb at the solid wall for a typical duration similar or larger than the total simulation time of 100 ns, i.e., for much longer time than the typical adsorption duration of water molecules (τ A ≈ 40 -100 ps (Fig. )). The presence of ions in the solution, and their adsorption at the solid surface, induce several changes in the structure and dynamics of water near the interface. For instance, density and orientation profiles of the water molecules at the surfaces are modified (Fig. bc), the typical rotation time τ R of water next to the interface increases (Fig. ), and the typical adsorption time of water at the solid interface decreases.