> We should implement something like pressure. Is this even possible?

Possible, yes, but complicated in detail. As CK mentioned I have "a" solution in the works that I will finish eventually. Hopefully somewhere this year, if I find the time.

Concerning ways water disappearing: You really shouldn't look into real world mechanics, because water is even more annoying there. Once you are underground, you won't have any evaporation anymore - instead you have seepage. And then you quickly have aquifiers. Many real-world tunnels have to pump water all the time just to keep the underground water out.

That said, I'm actually somewhat a fan of adding seepage. I always objected to a few pixels of loam holding back kilometers of water pressure... But it would make life a lot harder for miners, that's for sure.

(And concerning evaporation - I think we already have something like that with the rule that holds sea levels constant.)