Why can you not use a different mesh with unity water

Hi
So this has bugged me for a while thought i would see if any one has an explanation for why this is.
If you substitute the provided mesh with any other it fails. Now with this in mind i have imported said mesh into blender pretty much destroyed it i reduced it to a square with only 4 verts reunnwrapped it in every way possible and it still works!.
But heaven forbid you make an exact copy in blender and try use it will fail hard.

So the question is why what makes the mesh so special??It makes no sense .Has anyone ever managed to use a different mesh to work with the water???How did you manage it?

Did you change the mesh filter on the water prefab to the mesh you wish to use?