Originally Posted by
SASless
How accurate is water just falling straight down the hole in determine the equator?
It's bunkum. Water prefers to spiral down a plughole, but at the scales we're talking about the Coriolis force is far too small to be relevant. Assuming you live a reasonable distance from the equator, you can demonstrate this quite easily. Fill a basin with water, remove the plug and swirl the water in one direction with your hand to encourage it to spiral that way. Now repeat, but in the opposite direction. Unless you have a spiral basin, you should see that both work equally well.
In one of his travelogues, Michael Palin had a demonstration from a guy in an equatorial country showing the water spiralling down a funnel in opposite directions either side of a line drawn on the ground that was allegedly along the equator. It was pretty clear that he ensured it spiralled in the correct direction by the way he poured it into the funnel.
It works well for weather systems, which is why equatorial regions are dominated by the Doldrums.