Rooting hormone would do it good, but to get it fast and good in no time, get yourself an aquarium air pump, air line and an air stone and put it in the water. You wont have to change the water out as it will not rot and the constantly oxygenated water will cause you to get roots in no time. Its almost fool proof and the easiest way to clone, in fact its so easy, you will land up getting carried away so you have to pace yourself.