Dam

A dam is a artificially constructed barrier which obstructs, redirects, or slows down the flow of water. The main purpose of dams is to retain water which can them by used by a populace.

During the establishment of the Nisus science colony, a gigantic dam was placed near the colony so that the inhabitants would have fresh water, as well as aiding in the creating electricity via the colony's power plant. (TOS novel: The IDIC Epidemic).