Hydro electricity is power generated by harnessing the power of moving water. Not necessarily falling water, just moving water. There are many famous such generating stations in the world, not the least of them at Niagara Falls, Grand Coulee and Boulder Dam. These are just a few of the many examples of energy produced by falling water.  Any steady current of flowing water from a river or other waterway can be converted to power.

The Hydro Electricity extracted from water depends not only on the volume but on the difference in height between the source and the water's outflow. This height difference is called the head. The amount of potential energy in water is directly proportional to the head. To obtain very high head, water for a hydraulic turbine may be run through a large pipe called a penstock.

For example, energy is derived to make power by the force of water moving from a higher elevation to a lower elevation through a large tube" otherwise known in technical terms as a "penstock". When the water reaches the end of the penstock, it turns a water wheel or "turbine" at enormous speeds. The turbine rotates, through a connected shaft to an electrical generator, and this generator creates electricity. It is the turbine and generator working together that converts "mechanical energy" into "electric energy". The water that makes this possible, is a renewable energy resource, just like the wind that turns the turbine attached to a generator.