reservoir

n. 1 large natural or artificial lake as a source of water supply. 2 receptacle for fluid. 3 supply of information etc. [french: related to *reserve]

n. A place where anything is kept in store; especially, a place where water is collected and kept for use when wanted, as to supply a fountain, a canal, or a city by means of aqueducts, or to drive a mill wheel, or the like.