Travel Myths: Water Drains the Opposite Direction in the Southern Hemisphere

In his Travel Myths column, Brian Biros will be debunking common misconceptions about travel, with topics ranging from toilets to terrorism. No myth is safe.

Maybe you learned about it when Bart Simpson called collect to Australia to see if it was true. Or maybe you saw it in effect on Michael Palin's documentary Pole to Pole or you heard it from someone who watched one of these programs, or they referenced the spinning of hurricanes and cyclones. Any of these scenarios would leave you with the following conclusion: the water in toilets and sinks spins the opposition direction in the Southern Hemisphere.

However, in today's internet age, most search results will tell you that's not true. The topic has been barstool trivia for decades, but is it all just a big myth or is there some truth to it? To find our answer, let's look to something that these days has become a bit of a forgotten science: Science.

The Coriolis Force

The origins of our conundrum date back to 1835, when French scientist Gaspard-Gustave de Coriolis first mathematically documented what is now called the Coriolis force, which, according to Merriam-Webster dictionary, is:

An apparent force that as a result of the earth's rotation deflects moving objects (such as projectiles or air currents) to the right in the Northern Hemisphere and to the left in the Southern Hemisphere

When this force is applied to an object, the result is called the Coriolis effect. It gets even more complicated, dealing with changing distances between latitudinal lines, gravity, low pressure systems and enough physics to make your head spin, however, you really just need to look at the most popular example of the Coriolis effect to know it's true: hurricanes. In the Northern Hemisphere, they spin counter-clockwise. Their counterparts in the Southern Hemisphere, called cyclones, spin clockwise.

An Experiment

Now let's shrink this down to something that will fit in your bathroom. In theory, the same physics should affect a draining sink or toilet, but how does this work in practice? Luckily, I had previously traveled to Uganda and recorded the science in action — I paid this man $2 to conduct an experiment in which I watched water drain in the Southern Hemisphere, Northern Hemisphere and directly on the equator. See what happened in the video, below.

There you have it! Indisputable proof from a Ugandan man, obviously a scientist, that drains rotate differently on opposite sides of the equator. He even offered to sell me a certificate for an additional $2 stating I had witnessed this "geological geographical water experiment" at the equator (I passed). But if our scientist friend, who also sells Uganda refrigerator magnets, has shown this to be true, why does the internet say it's false?

Debunked

The truth is, while the Coriolis effect does technically impact a sink or toilet draining, the effect is only noticeable over great distances or at high speeds, such as hurricanes. Other conditions, like initial spin (even if left to sit for a while) or imperfections in the water basin would far outweigh the Coriolis effect on a small sink or toilet draining over a short period of time. Even in perfect conditions with no initial spin or external factors, the Coriolis force would only be strong enough to cause roughly one rotation per day of the water — nothing that is observable in the short time a sink or toilet would drain.

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Most toilets in the USA do drain counter-clockwise, but this is simply by design. Jets shoot the water out at an angle, giving it a strong initial rotation on which the Coriolis effect is negligible. In many other countries, the most common way for a toilet to flush is straight down with no rotation. Additionally, a third of the world has no access to advanced sanitation — such as flush toilets — so it would be difficult in these parts to test this theory. Bottom line: There is very little hard evidence to support this myth and it has survived all this time just as a legend.

But What About the Experiment?

A closer look at the video shows one big flaw in the results. The water drains counter-clockwise in the Southern Hemisphere and clockwise in the Northern Hemisphere — just the opposite of what it should be doing according to the Coriolis effect. Also, objects need to be much further away from the equator for the Coriolis force to have any effect on them. I should also mention that a guidebook noted that the actual equator, according to GPS, is about 50 feet from this equator monument, meaning all three "experiments" were actually conducted in the same hemisphere. I want my $2 back.

If you're now wondering how this hoax works, let's take another look at the video. We know that any initial force on the water would far outweigh the minuscule Coriolis effect. The metal blade our scientist-turned-charlatan inserts to stabilize the water actually does the opposite. Watch at the 0:19 mark, where he very subtly turns the blade in a slight counter-clockwise direction as he removes it, giving it a small counter-clockwise momentum that continues as it drains out. At 1:27, he puts a slight clockwise momentum on the water as he removes the blade. And at 2:29, he very carefully lifts the blade straight out to make sure no initial conditions are placed on the water, and it drains without rotation.

So How Did the Myth Persist for so Long?

The "experiment" I witnessed is similar to what Michael Palin recorded at the equator in Kenya in the BBC documentary Pole to Pole. He never mentions it's a fraud — in fact, it doesn't even appear he knows that it is. The program debuted in 1992, meaning the internet wasn't around like today to quickly fact check this.

The Simpsons episode, which develops into a scandal around an international collect call to Australia to find the answer, also purports that toilets flush the opposite direction in the Southern Hemisphere. Granted it is a cartoon, but toilets spinning counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere is presented as a fact by Lisa, the Simpson we are supposed to believe. Again, this episode debuted in 1995 when the internet was in its early days and Snopes and Google weren't around to ask.

I've read reports that the myth has also appeared in text books and was commonly passed along from teachers to students in grade schools and high schools. I specifically remember the topic coming up in one of my (non-science) high school classes in 1999, and a student was sent to the library to search the internet for the answer. He returned 20 minutes later with a printout from a website saying toilets do indeed flush the opposite direction in the Southern Hemisphere.

Closing the Lid

Thankfully, we live in a world today where we can believe everything we read on the internet. Okay, well, maybe not, but at least when it comes to science, the answers are out there and pretty easy to come by as long as we consult scientific sources. The coolest experiment I came across while researching the Coriolis effect was two YouTube videos from the USA and Australia that are to be watched simultaneously conducting the same experiment while draining a kiddie pool in each country. In this controlled setting with a much larger volume of water, the Coriolis effect is actually visible on a minor — but definitive — scale. You can watch them here and here.

However, our initial proposition does remain a myth. Toilets don't flush the opposite way in Australia and water doesn't drain in opposite directions on either side of the equator no matter how far you are from it. We can now safely flush this myth down the drain. Forever.

All images courtesy of author unless otherwise noted.

Brian Biros is a veteran backpacker who has explored nearly 100 countries on a budget using points and miles to fly for free. He began contributing to The Points Guy after winning the "Into The Blue: Marathon to a Million" photo contest and scavenger hunt. Follow along with his travels on Instagram and read tales of his misadventures at www.biruvia.com.