I was messing about and experimenting and I came up with an example of how to make realtime reflective water. It would probably make a good screensaver with a little editing.
Anything in the top half of the frame is reflected in the water below and distorted by animated waves. To see the realtime reflection, pressing the left mouse button will set off a firework in the sky, and also the glowing green pointer itself will be reflected.
It uses the Viewport object for the reflection, the Lens object for the distortion, and also the Perspective object which isn't important but adds a nicer effect of depth.