Definitions for water power
Random House Webster's College Dictionary
the power of water used to drive machinery.
a waterfall or descent in a watercourse capable of being so used.
a water right possessed by a mill.
Origin of water power:
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
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