This was a neat idea for the theme. I love seeing what you guys come up with when some pressure is applied.
The game felt like there was enough difficulty throughout the time that I played it. I think it would be nice to see the water vapor start to collect together a little more so it is just a hair easier to navigate pass each of the branches and it would mimic how actual water collects together.
Also, I would put a high score indicator at the end of the game so you can track your progress; this will help your replayability.