Attention! I'm releaving my biggest commercial secret now! Merge black waterdrops with white background and apply Blur to it. Radius is important, feel free to experiment. I chose 7 px.

Condensed - Making Of - Step 11

And now, hit Ctrl-L to open Levels dialog, and move black and white arrow pointers closer to the middle. You'll see how our blurred waterdrop become sharp and smooth.

Condensed - Making Of - Step 12

Remove white from this layer. You can use the following shortcuts for that:
* Ctrl-A
* Ctrl-C
* Q
* Ctrl-V
* Q
* Del

(this was another professional secret! :-))

Condensed - Making Of - Step 13

Now it is time for nice layer effects. Set layer blend mode to Screen, and use Shadow, Bevel and Inner Glow to make waterdrops look better.

Condensed - Making Of - Step 14

Some more lights and reflections would make our artwork much nicer. Create new layer (with blend more = overlay and opacity = around 50%), select brush tool and white color, and spend another hour putting white dots where light is reflecting in the top of waterdrops (in my case, light is falling from top).

Condensed - Making Of - Step 15