The Debunker: Does Water Really Drain Differently Below The Equator?

by Ken Jennings

If you’re in the Northern Hemisphere, August is, just like the human body, at least 60 percent made of water: vacations to the beach, weekend trips to the lake or pool, big pitchers full of refreshing ice water. August is also National Water Quality Month, as you probably know, and it’s when we all have our big get-togethers to celebrate World Water Week (August 26-31!) and Sea Serpent Day (August 7). It may be hot and dry where you are right now, but at least Ken Jennings can make it rain knowledge with his August Debunker column, deflating everything you think you know about H2O.

Water Myth #2: Bathroom Fixtures Drain the Opposite Way in the Southern Hemisphere.

Fans of TV’s The Simpsons may recall the 1995 episode in which ten-year-old Bart creates an international incident by calling Australia to confirm the commonly held belief that the rotation of the Earth makes toilets flush clockwise in the Southern Hemisphere but counterclockwise in the Northern Hemisphere. (Fleeing corporal punishment from the Australian parliament, Bart later seeks refuge in the American embassy there, where he finds that plumbers have installed devices in the toilets to make them “swirl the correct American way...”)


This idea has been tested by scientists since 1908, and was popularized by a 1962 article in Nature magazine called “Bath-Tub Vortex.” In that experiment, a 300-gallon tank of water was allowed to settle for 24 hours, so as to be absolutely still. When a central plug was removed the next day, tiny chips of wood revealed that the water did, indeed begin to rotate counterclockwise after about fifteen minutes. This is consistent with the “Coriolis effect” caused by the Earth’s rotation, the same phenomenon that makes storms rotate opposite directions in the two hemispheres.

Unfortunately, bathroom sinks, tubs, and toilets are much smaller than hurricanes, and any possible Coriolis influence is mathematically insignificant compared to other forces that might create a drain vortex, like currents in the water or irregularities in the container shape. Water can drain either direction in either hemisphere, in other words, unless you go to great lengths to cancel out all other factors except the rotation of the Earth. Unless your toilet is mathematically perfect, it probably goes both ways.

Quick Quiz: What’s the most populous country located entirely in the Southern Hemisphere?

Ken Jennings is the author of Brainiac, Ken Jennings's Trivia Almanac, and Maphead. He's also the proud owner of an underwhelming Bag o' Crap. Follow him at ken-jennings.com or on Twitter as @KenJennings.

Photo by Flickr member peapod labs. Used under a Creative Commons License.