In addition to explaining partially charged interfacial ions, our observation of excess charge in interfacial water seems as well the only possible explanation for capacitance values of ∼ 24 µF/cm 2 that were reported for Pt(111) covered by static interfacial water and biased by adding interfacial protons . In a in classical plate capacitor picture with ϵ = 1 (static interfacial water), C = 24 µF/cm 2 can only be explained by ion-substrate distances of ∼ 0.4 Å which is completely unrelated to the system's atomic structure. Instead, the extended electronic charge distributions of Fig. a naturally yield according values for realistic positions of ions e.g. at a distance of around 2.2 Å as demonstrated in Fig. b. Here we report expected capacitance values C bias = ∂σ ∂ϕ bias for ϕ bias derived via eq. 1 using the prototypical electron distributions ρ corrected electrode and Gaussian counter-ion densities ρ counter as indicated in Fig. a. While certainly oversimplified, this analysis nevertheless clarifies that the FF-intrinsic electron distribution can only lead to unrealistically small, static capacitances (< 3 µF/cm 2 ) equally as the generic electron spillover at Pt(111)-vacuum interfaces (< 10 µF/cm 2 ). In contrast, DFT-derived electron distributions for Pt(111)-water interfaces readily explain values of ∼ 24 µF/cm 2 for meaningful counter-ion distances and smoothly converge to a value of ∼ 5 µF/cm 2 when counter-ions are placed at the furthest extent of interfacial water (∼ 5 Å). The latter case essentially corresponds to and thus explains the capacitances observed for Pt(111) covered by a single static water layer and biased in an implicit solvent environment (C ∼ 6 µF/cm 2 ), for which also very similar excess charge distribu- tions on interfacial water were observed (cf. Fig. in Ref. ). In summary, a significant amount of excess electrons localizing within interfacial water in the spatial region z = 2.5-5.5 Å above a Pt(111) surface seem the most compelling and simple explanation for the a range of observations made in the literature that cannot be rationalized otherwise, e.g. with traditional ideas about interfacial charges residing exclusively on the metal electrode part of the system. Most importantly, our analysis indicates that this partial metallization of interfacial water is not connected to the existence of ions, i.e. it does not derive from electrons shared between interfacial ions and their solvation shell , but rather from electrons shared between the metal and interfacial water.