wa·ter·pow·er 
(wôtər-pou′ər, wŏtər-)
(wôtər-pou′ər, wŏtər-)n.
1.
a. The energy produced by running or falling water that is used for driving machinery, especially for generating electricity.
b. A source of such energy, as a waterfall.
2. A water right owned by a mill.