Or it could work like this:
[This doesn’t make water finite, but it solves the world flooding]
Water is allowed to spread on top of any other block, and always down.
Water is only allowed to spread on top of
existing water if that layer of water isn’t connected to the ocean, and if there are no empty gaps around that
layer.
“Connected to ocean” can either mean directly or indirectly via a (series of) waterfall(s).
