It is misconception that if rudraksha sinks in the water then it is original and if it floats then it is a duplicate.
Many people get confused with the shape and size. One should not worry about it. Just see that the Mukhi is well defined, corns and contours are natural, there are no cracks near the central hole and the bead has a good health.
To test the originality of Rudraksha, boil it for continuous 6 hours, if it is real there won’t be any affect on the Rudraksha bead. If it is artificial or two rudraksha are joined together artificially they will get separated.
The best way is to procure it from reliable source.