A water layer contains information about a water surface such as height level, texture, tiling, reflection, speed of waves, and so on.

Water is a simple plane object that fits the assigned zone, positioned at a height specified in the "level" parameter. By changing the "level" we can move the water plane up and down, intersecting the terrain.

Sometimes in 3D engines that use water planes, ugly z-fighting artifacts are visible in areas where the ground geometry intersects the water plane, usually in the middle. This effect is more visible the higher the viewer is relative to the plane.

Terrain geometry close to the water plane is near coplanar (lying in the same plane), as a result of mathematical inaccuracies this can cause parts of the z-buffer to "fight" for dominance.

Z-fighting...