Yes it is true. It is caused by the earths center of gravity, which is the core. Every thing on this planet and around this planet wants to got that way. the water in the sink in the northen hemisphere wants to go from right to left, because it is going, in effect, downwards. Where as in the southern hemisphere, it travelles the oppsite way. Because the direction to the earths core is in the opposite direction. Hope that makes sense. But thats how it works.