Magician tricks are often well kept in secret. There are many youtube videos that explain possible tricks to create the illusion. There are physical ways to levitate in air, but they would involve very advanced technology. For instance, walking over a superconducting floor and having magnets in you clothing, so the magnetic repulsion in the upward direction overcomes the gravitational force in the downward direction. Walking of water would be easier, but you will still need to add something because the unmodified human body cannon do it. You either get big shoes floating shoes (kind of a mini boat on each feet) and practice a lot so you don't fall down, or you can use "shoe" that takes advantage of the superficial tension of the water, like those insects that walk over water. They can because they do not "break" the water surface due to the detailed structure of their feet plus their tiny weight. I am not aware that such technology have been developed for humans, but it is certainly possible. This physical trick is fundamentally different to the one which I mentioned before that is based of floaters.
Now, if the question is if an unaided human can walk on water or levitate on air. The answer is a plain NO!