Hydroelectric dams produce electricity by using falling water to spin a turbine that is connected to a generator through a large metal shaft. The power that the generator receives from the turbine is converted into electricity and then transferred to homes and other structures through power lines.
Dams are typically constructed on large rivers that have a significant enough drop in elevation so that water is able to fall and enter the dams water intake. As long as there is enough water in the reserves directly behind the dam, water will continue to fall into the intake and travel through the penstock and reach the turbine. The hydraulic turbines used in hydroelectric dams create electricity by converting flowing water into mechanical energy.