Diverse water treatment technologies are widely applied to manage water quality, with ubiquitous hydraulic energy remaining. Emerging hydraulic pressure–electricity conversion, along with its in situ utilization, provides a promising strategy for addressing common challenges in water treatment, which is convenient, efficient, and practical. This innovative concept has garnered extensive interest and has achieved exciting progress over the past decade. Piezoelectricity, which induces charges via mechanical deformation, serves as a direct hydraulic energy harvesting mechanism to achieve force–electricity conversion, opening new avenues for innovating traditional water treatment technology while compensating for its shortcomings. However, such in situ hydraulic–electricity coupling is still in its early evolutionary stage and requires thorough investigation to determine future development directions. With this in mind, we discuss hydraulic piezoelectricity as a means of addressing common challenges in water treatment technologies, with a focus on representative membrane fouling, catalytic reactions, and sludge dewatering. Then, we further explore other emerging hydraulic-based technologies, such as hydrovoltaics, solid–liquid triboelectricity, and other energy methods, such as thermal energy, to expand the paradigm and scenarios of in situ electricity advancements in the water treatment process.