Hydropower, hydraulic power, hydrokinetic power or water power is power
Power (physics)
In physics, power is the rate at which energy is transferred, used, or transformed. For example, the rate at which a light bulb transforms electrical energy into heat and light is measured in watts—the more wattage, the more power, or equivalently the more electrical energy is used per unit...

 that is derived from the force
In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...

 or energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...

 of falling water, which may be harnessed for useful purposes. Since ancient times, hydropower has been used for irrigation
Irrigation may be defined as the science of artificial application of water to the land or soil. It is used to assist in the growing of agricultural crops, maintenance of landscapes, and revegetation of disturbed soils in dry areas and during periods of inadequate rainfall...

 and the operation of various mechanical devices, such as watermill
A watermill is a structure that uses a water wheel or turbine to drive a mechanical process such as flour, lumber or textile production, or metal shaping .- History :...

s, sawmill
A sawmill is a facility where logs are cut into boards.-Sawmill process:A sawmill's basic operation is much like those of hundreds of years ago; a log enters on one end and dimensional lumber exits on the other end....

s, textile
A textile or cloth is a flexible woven material consisting of a network of natural or artificial fibres often referred to as thread or yarn. Yarn is produced by spinning raw fibres of wool, flax, cotton, or other material to produce long strands...

 mills, dock crane
Crane (machine)
A crane is a type of machine, generally equipped with a hoist, wire ropes or chains, and sheaves, that can be used both to lift and lower materials and to move them horizontally. It uses one or more simple machines to create mechanical advantage and thus move loads beyond the normal capability of...

s, and domestic lifts
An elevator is a type of vertical transport equipment that efficiently moves people or goods between floors of a building, vessel or other structures...

. Since the early 20th century, the term is used almost exclusively in conjunction with the modern development of hydro-electric power
Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy...

, the energy of which could be transmitted considerable distance between where it was created to where it was consumed.

Another previous method used to transmit energy had employed a trompe
A trompe is a water-powered gas compressor, commonly used before the advent of the electric-powered compressor. A trompe is somewhat like an airlift pump working in reverse....

, which produces compressed air from falling water, that could then be piped to power other machinery at a distance from the energy source.

Water's power is manifested in hydrology
Hydrology is the study of the movement, distribution, and quality of water on Earth and other planets, including the hydrologic cycle, water resources and environmental watershed sustainability...

, by the forces of water on the riverbed
Riverbed may refer to:*Stream bed, the channel bottom of a stream or river or creek*Wadi, a dry riverbed that contains water only during times of heavy rain*Riverbed Technology, an American technology company...

 and banks of a river.