Water constantly move through a vast global cycle, in which it evaporates from lakes and oceans, forms clouds, precipitates as rain or snow, then flows back to the sea. The energy of this water cycle, which is driven by the sun, is tapped most efficiently with hydropower.
Impoundment Hydropower: uses a dam to store water (see animation to the left.) Water may be released either to meet changing electricity needs or to maintain a constant reservoir level.
Diversion Hydropower: Channels a portion of the river through a canal or a penstock but may require a dam
Pumped Storage: Pumps water from a lower reservoir to an upper reservoir at times when demand for electricity is low. During periods of high electrical demand, the water is released back to the lower reservoir to generate electricity.
Wondering how hydroelectricity is generated? Or where it comes from?
You can learn all about it with these demonstrations.