Creating a hydroelectric generator using an old firefighting pump may not be efficient, as most firefighting pumps are centrifugal and not designed for this purpose. A turbine is typically required for effective hydroelectric generation, although some pumps can function as turbines in specific conditions. The efficiency of the system would depend on the pump's specifications, including its type, height difference from the water source, and flow rate. While using inexpensive or free materials is appealing, the design must be well-matched to the site for optimal performance. Overall, while the concept is theoretically possible, practical implementation may face significant challenges.