Where does the phrase “to back water” come from and What does back water mean?

Literally, the phrase “to back water” was said of a ship, boat, canoe, or the like, to which the paddle wheel was reversed, or the oars or paddles were moved backward.

Hence, figuratively, one is said to back water when obliged to retract a statement or reverse a position or withdraw from a situation.

The expression dates from the early days of the steamboat, the early nineteenth century.