The coriolis myth

You may have heard, or you might even have been taught by your physics teacher, that the coriolis force is the rotational force that makes water rotate down the drain in one direction on the northern hemisphere and in the other direction in the southern hemisphere. However, I am sorry to tell you, it is a myth.
There is indeed a coriolis effect, and it does indeed affect particles in opposite direction on either hemisphere, but it is not strong enough to make the water run down the drain in a particular direction. The direction in which the water poured into the tub, the shape of the tub, and even small perturbance by objects in the tub all have a larger effect on the direction of rotation.

Read more about:
The Coriolis Effect - by wikipedia
Bad Coriolis - by Bad Meteorology
Does the water go down the drain...? - by Everyday Mysteries