Nice, original mechanic! I like how you made all the water drops animated, made the game feel more alive. You could have animated the portals as well. I particularly enjoyed seeing how the water drop's sprite changed according to the amount of water it had. You found a nice variety of puzzles, too.
Level 13 had free movement, I could go on top of green blocks and even outside the camera view. It's a shame there was no music or sound effects.
An interactive tutorial would have been better than the wall of text on the "how to play" section.
"Back to start" -button sounds like it goes to start of level, or back to the first level, so "Back to menu" or just "Main menu" would be my suggestion to change.