J. Hector St. Jean de Crevecoeur's "Letters from an American Farmer"

reservoir

/ˈrɛzə(r)ˌvwɑr/ (n)
a. A lake or large pool, natural or man-made, used to store water for public and industrial use, for irrigation, etc. Also more generally: a large expanse of water held back by a dam.
OED