I don't understand what you are talking about, but it's nice.
It boils down to reflections being a big fat cheat. If you think about what a reflected view is...
Cam \ /Light \ / \/(Boing!) - - - - - - - - - - - Water
...it becomes quickly clear that, rather than trace the light for each pixel you can just bung another camera in with an inverse pitch...
Cam + /Light + / +/ - - - - - - - - - - - Water / / / Cam2
The problem arises when you have something either partially or totally immersed in the water, because now the camera that generates our reflections will see things it should not...
Cam + /Light + / +/ - - - - - - - - - - - Water / ***** <-Hello, what's this? / Cam2
And this is why clip-planes are so lovely. Now you can tell the camera not to render things on either the near side of the clip plane or the far side. Stick a clip plane where the water plane is and Cam2 can now ignore anythng below the surface, giving a more accurate reflection...
/Light
/
/
- - - - - - - - - - - Water
<-
<-Nowt rendered. Top banana!
<-
Cam2