The Truth About Toilet Water Swirling Direction at the Equator

Have you ever wondered which way toilet water swirls at the equator? The age-old myth suggests counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere due to the Coriolis force. However, the truth may surprise you.

The direction in which toilet water swirls has more to do with the manufacturer of the toilet than any grandiose natural phenomenon. Let's debunk the myth and uncover the real factors at play.

The Coriolis force, influenced by Earth's rotation, does indeed affect the spin direction, but it's usually only noticeable on massive scales like trade winds and hurricanes. When it comes to your toilet, the Coriolis force is far too weak to have a significant impact.

In 1962, Ascher Shapiro, a fluid mechanics specialist at MIT, conducted an experiment that demonstrated the Coriolis force's minor effect on water drainage. He poured water into a dish, initially swirling it clockwise in defiance of Northern Hemisphere expectations. After allowing the water to stand for 24 hours, he observed that when the drain was unplugged, the water slowly started to swirl in the opposite direction. A different study from the University of Sydney confirmed the reverse effect in the Southern Hemisphere.

However, there's one crucial factor that truly determines the direction of toilet water swirl: the toilet's design. Specifically, it's the orientation of the flush jets. These jets dictate whether the water drains left or right, completely overshadowing the Coriolis force's negligible impact.

So, the next time you flush your toilet at the equator, don't worry about the Coriolis force. Instead, take a look at your flush jets—they hold the secret to the water's swirling direction.