way, the influence of χ S is removed. This is in contrast with the Wave Function (WF) method, where the workfunction is calculated explicitly, often by taking the energy level of the vacuum above the water film, which is not possible in our simulations. In this case, this vacuum level is assumed to be aligned with the absolute vacuum level and the value of such workfunction is directly compared to the accepted absolute value of the SHE (4.44 V). In this case the surface potential contribution is implicit and is assumed different from experimental values. As a result, the workfunction between both methods mainly differs by a constant shift. Interestingly, important discrepancies have been reported between experimental and calculated values of the surface potential χ S of water. Multiple experimental studies reported low positive values (≈ 0.13 V 103,112,113 ), while calculated values are often negative and large (-0.54 V 114 ) which Fawcett 103 mentioned as unphysical. This is the case for the RISM (TIP5P) model which predicts a surface potential in agreement with this value of -0.54 V. In this work we argue that only the difference of U • SHE and U M|S (abs) carry physical meaning: