Attached Link: Water transparency test .tgd

I'd like to clear this issue up. Although T2 has no transparency yet, the water is NOT postworked in my Rockpool image at all. The scene comprises of 2 renders, one for subsurface and one for the final render.(which includes the subsurface render in the process... I'll explain this shortly.

To begin with, we create our riverbed, texture it accordingly and then add our water and set the levels, roughness etc...
Once we've got to this point we will then DISABLE the waterplane and render the image 'dry'. A lower detail setting will suffice for this(.5 is good I find).
Once this image is rendered we save it as 'subsurface.bmp'. Now, go to your water nodes group and create a new 'imagemap shader'(select 'subsurface.bmp' as the image, AND a new 'merge shader', the merge shader is the key to  the transparency.
When we have both new shaders set in the water group we place the watershader into 'input A' of the merge shader and then the imagemap shader into 'input B', the output from the merge shader will now go to the input of your lake/waterplane. You will instantly see the transparency in the 3D preview window, the merge shader 'Mix to A' slider is now the fake transparency modifier. Sliding it left will make your subsurface image less visible, sliding it right will make it more visible.

What the merge shader does is actualy blends both the waterplane and the subsurface image together for the final render. No post proccessing is required.
I'll attach a quick basic water transparency example .tgd for anyone wanting to check out the settings if they wish.

For the record, and not to blow my own trumpet too much, I think my T2 version is still far more convincing and realistic looking than any of the Vue examples posted above, as yet...