After reading up on rendering reflections, it seems that the way to do it is the render the scene from underneath the plane of reflection, and then use projective texturing to map the reflected texture to the reflective surface. However, why can't you just use the image from rendering the scene underneath the water, and draw it upside down behind the terrain?
Here's what I mean: http://i.stack.imgur.com/g6VbX.png
The lines at the end of the views represent the drawn image, the colored dots are supposed to represent the corresponding points on the textures, and the brown is supposed to represent the terrain.
From the diagram, it would appear that you can just take the image rendered from the camera below the reflective surface, flip it upside down, and then draw it behind the terrain on the actual rendered image.
Is this another way to do it, or am I completely missing something here?