Triboelectrification is of great importance for many classical (petroleum, pharmaceutical, polymers) and emerging (generators, sensors) technologies. For energy generation, the contact area between the materials experiencing tribocharging is a key parameter: in addition to the nature of the materials, tribocharging scales with contact area. In this work, an approach is proposed to maximize tribocharging contact area by exploring the cycle of water intrusion–extrusion into–from hydrophobic nanopores with surface area orders of magnitude higher compared to flat or even nanotextured surfaces. Here this study reports the first experimental evidence of electrical energy generation upon water intrusion-extrusion cycle under bias voltage-free conditions. Combining these experiments with hierarchical molecular dynamic simulations/ab initio calculations, a microscopic mechanism of triboelectrification is hypothesized for water and grafted silica. The proposed approach provides a methodological alternative to studying solid–liquid contact electrification and an alternative root for a noticeable increase of specific contact area for solid–liquid triboelectric nanogenerators.