I'm re-rendering the pool at the moment, having added a terrain to give the water some movement (Thanks Baggins :) Your pic gave me the idea.) but alas, it's no longer transparent.
I'm guessing because it's 2 layers now, but on the other hand... I kinda like it better that way.
I haven't uploaded it yet (it's still rendering.) but I will for comparison sake when it's done. :)

Silke