i wont go into too many details, but the phenomenon is called total internal reflection. If the light in the water hits the water air barrier at the right angle, it gets reflected back into the water. It can do this over and over again, and thus "follow" the water

This is how fiber optic cables work

also, next time you see a fish tank, try to look through one end of the tank through another (i.e, look from the right side of the tank, into the tank, and through the front end of the tank). if you move around to the correct angle, you will notice that the inner glass of the tank looks like a mirror! this is the same effect

Yes. There are folks out there who make a very lucrative living by mastering the internal refraction physics that keeps light within a tube of water. The fountains at the Bellagio Hotel in Las Vegas are prime examples of this capability. They are gorgeous.

Oh, by the way, the patented process of creating coherent tubes of water (your bow) that can channel light is also amazing. The guy who did the Bellagio holds that patent. Sorry I don't remember his name, but he was featured one episode on Sunday Mornings on CBS.

yes. the water flow must be linear and non turbulent. also the stream should be thin enough to allow light to fall at a very narrow angle and get totally reflected inside the stream of water .