At 8 inches per mile, the earth curves at a little more than 1/1000 of an inch per foot. Bridges like the Danyang–Kunshan Grand Bridge are not one piece. This allows it to flex to the curvature of the earth as well as allows movement in the event of high winds or an earthquake.

As for water always forming a level surface, this is true. It is level in relation to Earth's gravity. It is not, however, a straight surface.