Certain idioms don’t need much of an explanation to make sense. If you’re “playing with fire,” chances are you’re metaphorically doing something recklessly that could bring severe consequences. If you’re “dropping your guard,” you’re lowering your defenses.

Other sayings are more difficult to parse. What does “falling off the wagon” have to do with excessive alcohol consumption? Does it refer to the loss of balance that accompanies inebriation? Did settlers tumble off wagons when they had too much to drink?

It actually has very little to do with any literal spills. The phrase “on the wagon”—which birthed “off the wagon”—has origins at the turn of the 20th century and was originally “on the water cart.”

Long before Prohibition, there was a grassroots movement to temper the perceived evils of alcohol. Organizations like the Anti-Saloon League formed that persuaded members to pledge their eternal sobriety to develop better character and set a good example.

Around the same time, it was common for cities to make use of water carts, or water wagons, which were large water tanks towed by horses. The water was used to moisten dusty streets and not really potable. Because of the prevalence of the tank, it became a kind of reference point for those discussing their commitment to sobriety. People said they’d sooner drink from the water wagon than accept a stiff drink. That soon evolved into proclaiming that a person was “on the water wagon.”

Once someone hopped on the proverbial water wagon, it followed that a lapse in their devotion would see them fall “off” the water wagon. As water wagons began to disappear from sight, it simply became “wagon.” Whether one was on or off described their current approach to drinking.

Of course, given the right circumstances, it is still possible to fall off the wagon both metaphorically and literally. All you would need is a wagon and way, way too much booze.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.