water power

from The Century Dictionary.

• noun The power of water employed, or capable of being employed, as a prime mover in machinery; hence, a fall or descent in a stream capable of being utilized for mechanical purposes.

from the GNU version of the Collaborative International Dictionary of English.

• The power of water employed to move machinery, etc.
• A fall of water which may be used to drive machinery; a site for a water mill; a water privilege.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Any source of energy derived from running or falling water; originally obtained from a waterwheel immersed in a stream; modern hydroelectric power is obtained from turbines fed from reservoirs

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the power to do work that is latent in a head of water