You have to do it exactly as I did, so check out the sample carefully. The default shader's output shouldn't be going into the water shader like you did. Furthermore; default shader color should be black! (can't see if you did), but the opacity tab is good like you did.
If you rightclick on a plane (or any shader) you get an option 'edit internal network' (or something like that), choose that. Now make some shaders in there, then go out of this object or shader (level up), and rightclick on the input node you want to link one of the new internal shaders to. Got it? If you do, that red triangle dissappears, and the internal shader is linked. That's one thing that's handy to know. The other is that if you make a new node next to your object (plane in this case), and go internal (in the plane), you can in the same way change the link to the shader that's next to the object/plane. Then an outside red triangle will appear and the shader is connected.
