Hydropower is considered a renewable energy source because it does not consume any water, only using kinetic or potential energy from the water to generate electricity. A technology is considered renewable if the fuel can be perpetually created or recreated.
Hydroelectricity is designed to take advantage of the substantial amounts of energy in running water. All moving objects have kinetic energy that can be extracted.
Traditional water turbines are installed on rivers to turn this energy into usable electricity. Dams make use of not only kinetic energy, but potential energy as well. By creating a large vertical gap, called the head, more energy can be harnessed.