Very cool game! I left a review on the jam submission page and I also read through the dev log cuz I was interested in seeing what went on behind the scenes. In a short amount of time, I think you nailed the arcade game loop perfectly regardless of the amount of content present--I never knew how much I needed a game like this until now.
As for the level design, I thought it was fine (no complaints). The 4 layouts were distinct enough to not feel repetitive, and the strategy aspect of wanting to save more water for a better end-of-level bonus helped keep the levels fresh in how they are approached even after playing them multiple times.
Adding new mechanics and enemies would have been interesting; like for example, an enemy that slowly dries up a wet tile (defeated by jumping on them) or a bomb-type object that wets multiple surrounding tiles at once. There's a lot of possibilities for such content, and it would be cool to see an expanded version of the game with new levels and mechanics.
Overall, excellent work!