Long-Distance Specular Reflections Illustrate a Lack of Curvature

A flat and level reflective surface is required for an accurate specular reflection, due to the fact that the angle of incidence is directly tied to the angle of reflection.
This allows the image size and shape to remain consistent with the object, within the specular reflection.

On the other hand, any reflective surface that exhibits convexity or concavity will greatly distort the image by magnifying, diminishing, and altering its orientation, due the the angle of incidence.

Specular reflections are an illustration of the flat nature of the surface of water.