Electrochemical processes at water-titania interfaces in TiO₂ thin films were studied using conducting-tip atomic force microscopy. Mesoporous titania thin films were prepared by sol-gel synthesis from molecular precursors with the addition of surfactants to induce the formation of a porous structure. We found that both three-dimensional local resistance and topography are significantly and irreversibly changed in the submicrometer range by applying a constant bias voltage, with water playing a fundamental role in this process. The mesoporous structure enhances these effects due to the highly water accessible porous titania surface, which can be easily tuned by changing the synthesis procedure. Our findings are important in the development and performance of titania-based electronic microdevices and could pave the way toward the design of new electrochemical lithography methods.