It's cute, and nothing wrong with a simple gameplay loop, but I have a few notes.
First, the lack of feedback on how close you are to the next level makes progress not feel very impactful, and means it's never really clear if it's a good idea to spend water for an upgrade or hold it to progress to the next level. Perhaps have the top bar fill up gradually as you approach the next level, similar to building the energy bar?
Regarding the energy bar, because it gradually fills as you tap and empties when you don't, for a long time I thought the way it changed to "5x Boost" meant that I was getting that boost as long as I kept clicking to keep the bar filled; I didn't realise it mean that I'd _charged_ a temporary boost, and that I needed to click the button to actually activate it. That could be better communicated.
Finally, it's just a bit too slow past the first couple of levels. Even with upgrades the idle progression is slow, and even with a fast auto-clicker and constantly boosting leveling still takes a long time, especially once you get to about level 10. If you can level up to the point of filling an ocean, I can't imagine how long it must take to do that!
If this is meant to be a breezy simple cute time-filler, the level requirements could be cut down a lot to make it a neat bite-size experience. If it is meant to be a bit more chonky, it probably needs another mechanic or two players can use to keep up with the increasingly level requirements. Maybe some upgrade which lets you reset your Tap upgrades for a multiplier to Idle to help it keep up and give more for a player to do? Or a second resource that's built up by keeping droplets instead of spending them that can be used for separate upgrades, to make for a choice on when to spend water for a prime upgrade compared to keeping it to build that other resource? And maybe there should be some small benefit to each level, to make the choice to spend on a resource or save for a level mean something?
I don't know, just spitballing!