Water always swirls (when going down a drain) in the same direction, as long as you stay in the same hemisphere. In the northern hemisphere, water always swirls clockwise and in the southern it always swirls counterclockwise.


    So if you ever get randomly teleported to a random location on earth, you can use a bit of water to figure out your [very] rough location.


    [This only works 100% of the time under perfect conditions]