Hydropower, or water-power is power that is generated from the energy of moving water, which may be harnessed for many useful purposes.

Before the availability of commercial electric power became widespread, hydro power was used for irrigation, and used to operate various machines, such as watermills, textile machines, sawmills, dock cranes, and domestic lifts.

Hydropower is one of the oldest methods used to harness energy, and has been used for hundreds of years. Water wheels and watermills were built in India; water powered mills produced flour from grain in Imperial Rome, and were also used for sawing timber and stone.

The power generated from a wave of water released from a tank was used to extract the metal ores in a method known as hushing. This was extensively used in Britain in the Medieval and later periods to extract lead and tin ores. The same method later evolved into hydraulic mining when used during the California gold rush.