Waterpower is energy created by moving water, especially when that water flows or falls from a higher place to a lower one. For thousands of years, people have harnessed waterpower to do useful work: turning waterwheels to grind grain into flour, sawing lumber, or powering textile mills that wove cloth.

The basic principle is simple but powerful. When water flows downhill or rushes through a narrow channel, it carries tremendous force. A waterwheel placed in a stream catches that force with wooden paddles, and the wheel begins to turn. That spinning motion can then power machinery through a system of gears and belts. Before steam engines and widespread electricity, waterpower ran factories throughout Europe and America, transforming how goods were made and accelerating the Industrial Revolution.

Today, waterpower generates electricity at hydroelectric dams. Water held behind a dam falls through large pipes called penstocks, spinning massive turbines that produce electrical power for homes and businesses. The water itself isn't used up in this process: it simply flows past the turbines and continues downstream. A single large dam can generate enough electricity to power an entire city, making waterpower one of the world's most important renewable energy sources.