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Evaporation‐driven electricity generators have been proposed to generate electricity by water interacting with nanostructured materials. However, several proposed mechanisms, such as intrinsic gradient of polar functional groups principle and electrokinetic effect perspective, are in wide discrepancy. Here, through the combination of theoretical calculations involving time dimension on material's moisturizing process and experimental analyses, it is revealed the working principle through the water molecule triple roles in driving moisture electric generators (MEGs): 1) intrinsic H2O absorption on the material surface and splitting into hydroxy group and proton due to the polarizability of the material surface determined by the static electric potential of the materials. This process induces the electrochemical potential difference of the materials via the work function changes; 2) freely diffused protons derived from the H2O splitting work as the ions charge carriers; 3) via the hydrogen bond of the water molecules to drive charge carriers diffuse between opposite electrodes, maintaining the internal circuit current flow. It is successfully unveiled that anatase TiO2 based materials for output voltage changes correlated to the domains' work function's difference, tuning by the surface adsorption species (H, Cl, OH) and anisotropic exposed crystal facets of the material. This work unveils MEG's general working principle. [ABSTRACT FROM AUTHOR]