The concept is interesting, but the writing seems lazy and most definitely could have some improvements.
In my opinion, it'll be more interesting if the protagonist is not an isekai MC #48762, but a bona-fide minor spirit who was born at the same time as the planet. And as time passes, he gains consciousness, grew more powerful and eventually all the "water" in the world are part of him. That way, he'll amasses an exorbitant amount of knowledge and wisdom as he walked through the passage of time, in which at one point he would be regarded as the "Primordial Water Spirit". But then for "unknown" circumstance, he got sealed in that lake.
A fuck ton of Isekai stories nowadays like having "Isekai-ed MC" just for the sake of it, while serving no real purpose at any point in the story besides a convenient tool in the beginning to "skip some things".
It's downright lazy storytelling and writing. Sorry for the rant, just gotta let this out of my chest.