Sorry for the delay in replying. Here is how I have it setup (now with pictures! thanks):
I have 1 main water tile, 1 main light grass tile, 1 main sand tile, etc.
Everytime I want to switch from mapping water->lightGrass to water->sand for example I need to repick the water tile on the second terrain (blue arrow). See image below.
If this is wrong and there is an easier way I am all ears :D. I just thought this is the only way since it does not seem to let me use the full water tile on multiple terrains. I have to redo it each time I need to use that terrain.