Post-mining land in the form of a former pit (void) is one of the environmental legacies of open-pit tin mining that, if properly managed, can be transformed into a productive asset. This study analyses the economic value of utilizing void water from the PT Timah Tbk tin mine, Pemali Unit, Bangka Regency, as an energy source for a Micro-Hydro Power Plant (PLTMH) to support the energy sustainability of surrounding communities. A quantitative-descriptive approach was applied, combining primary data (water-quality testing, field observation, and a purposive-sampling questionnaire of the affected community and mine employees) with secondary data (climate records, company documents, and PLN electricity tariffs). Technical calculations show that the void, covering 55.43 ha with a reliable discharge of 1.1145 m³/s and an effective head of 13.5 m, can generate 112.17 kW of power, or 982,632 kWh of energy annually, enough to supply approximately 600–800 households. Economic feasibility was assessed with the extended Net Present Value (extended NPV) method covering direct and external benefits and costs from 2009 to 2025 at a discount rate of 5.82%. The results show a direct benefit value of Rp20,550,110,104, a direct cost value of Rp15,506,962,790, an external benefit value of Rp822,466,682, and an external cost value of Rp767,635,570, producing a positive total economic value of Rp37,647,175,146, indicating that the plan is financially and environmentally feasible. Socially, 92.5% of respondents supported void utilization for PLTMH, 89.2% expected a stable electricity supply, and 56.8% expected increased income, confirming that the project can strengthen community energy independence while restoring the ecological function of the mined-out void.