The water typically flows from a higher to a lower elevation. These turbines are connected to electrical generators, which produce the power. The efficiency of such systems can be close to 90 percent. Hydro means water. This is changed to mechanical energy in a power plant, which is then turned into electrical energy.
Water is stored behind a dam in a reservoir.
In the dam is a water intake. This is a narrow opening to a tunnel called a penstock. A turbine is similar to the blades of a child's pinwheel. But instead of breath making the pinwheel turn, the moving water pushes the blades and turns the turbine. The turbine spins because of the force of the water.