I'm sure (hope so) that there is room for improvement in the water shader to make it more generally useful.
However a couple of things to remember about the water shader, firstly that the transparency has no end point or thickness. ie you can not have a piece of glass 5mm thick or a foot thick for example. The ray from the camera will be deflected each time it passes through a water/transparent polygon. This means that it will be deflected twice per polygon if you have double sided switched on. Your depth will need to be something huge, beyond the distance to the surrounding background sphere. anything less and the transparent surface will be opaque when viewed against the sky.
Think of it like this. If you hold a piece of glass up in front of you, perpendicular at eye level out doors you can see through it to both near foreground, a couple of meters away and the distance horizon and beyond, several thousand or hundreds of thousands of meters away. In Terragen this is not properly implemented at the moment. The transparency is intended only for shore lines and water edge effects where in almost every case the observer is above the water surface looking down to see a surface beneath the water. Therefore the light ray only gets refracted the once and then comes to a hard stop.
I understand how this works but its a little hard to communicate.
Remember to take all the wave variables to zero and set the transparency to something pretty high like 99%+ and the depth to something HUGE.
Hope this helps
Richard