You are correct that the FH map maker already comes custom with a waterfall mesh.
You can do this by going to the Mesh tab in Object Maker and type Waterfall1.mesh and a waterfall should appear.
here is a visual representation if you have a hard time too
http://www.youtube.com/watch?v=HH_27i42u4g (http://www.youtube.com/watch?v=HH_27i42u4g)