<p>This work presents a novel and rigorous framework for extracting gravitational potential energy stored in hydrostatic water columns using an advanced piston-based mechanical system. Combining classical hydrostatic theory with modern stratified fluid energy concepts, we describe the transition from Available Potential Energy (APE)—the portion of a fluid’s potential energy that can be converted into mechanical work—to Background Potential Energy (BPE), the minimum gravitational potential energy state the fluid can reach after mixing or redistribution of its mass. The system also incorporates innovative reset mechanisms, including pulley-canceled forces, where side pistons connected via a pulley system apply equal and opposite forces to neutralize the load on the front piston, and air-assisted actuation. We derive a new general law for hydrostatic energy depletion, and show that the system efficiently harvests available gravitational energy, achieving net-positive energy conversion cycles, as confirmed by experimental validation, while maintaining mass conservation. This approach opens a new frontier in gravitational energy extraction from static fluid reservoirs, bridging fluid dynamics, thermodynamics, and mechanical engineering.</p>