A widely held belief suggests that water drains differently in the Southern Hemisphere, particularly in Australia, compared to the Northern Hemisphere. This idea often involves water supposedly swirling in the opposite direction down drains and toilets. Exploring the factors influencing water movement can clarify this common misconception.
The Common Belief
Many people believe that water flushes “backwards” or in the opposite direction in the Southern Hemisphere, including Australia, when compared to the Northern Hemisphere. This widespread myth often attributes the supposed phenomenon to the Earth’s rotation, referencing a concept known as the Coriolis effect. The misconception suggests this rotational force is strong enough to dictate the swirl of water in small basins like sinks and toilets. While the Coriolis effect is a real scientific principle, its application to everyday water drainage is where the misunderstanding arises.
The Coriolis Effect Explained
The Coriolis effect describes an apparent deflection of moving objects when viewed from a rotating frame of reference, such as the Earth. This effect influences large-scale phenomena like global wind patterns, ocean currents, and the rotation of hurricanes and other storm systems. For instance, it causes hurricanes to spin counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. The magnitude of the Coriolis effect increases from the equator, where it has no effect, to the poles.
However, the Coriolis effect is weak on small scales and requires significant distances and time to become noticeable. It is too subtle to influence the direction water drains from a sink, bathtub, or toilet. Forces within a draining basin, such as the initial movement of the water or the design of the plumbing, are more powerful than the force exerted by the Earth’s rotation at that small scale. While the Coriolis effect impacts vast systems, it does not determine the swirl of water in your home drain.
What Really Influences Water Drainage
The factors determining the direction water drains from a basin are localized and more impactful than the Coriolis effect. The design of the plumbing and the basin itself play a significant role. For example, the angle of water jets in a toilet bowl or the shape of the drain can direct the water’s initial movement, creating a swirl. Even a slight initial swirl imparted by filling the basin or a hand moving through the water can dictate the direction of drainage.
Imperfections in the basin’s surface or whether it is perfectly level also influence the water’s path. These factors override any effect of the Coriolis force at this scale. Consequently, both clockwise and counterclockwise draining can be observed in either hemisphere, as the direction is primarily determined by these immediate, local influences rather than the Earth’s rotation.