In general, I would like to have water physics close to real - so that rain fills ravines, pits, wells, floods basements if they are from the soil. So that water gradually penetrates through porous blocks (earth, sand, gravel) and goes to sea level. Retained by impermeable blocks (stone, clay).
Then some caves will be flooded (or only after rain). It will be very cool to get trapped underground because of rain.
In general, from this you can go further in different directions: aqueducts, field irrigation, wells, storm drains, drains, dams, canals, locks, water wheels.
The player will be forced to carefully choose a place for construction and building materials so as not to have a headache later. Life in a dugout will sparkle with new colors.
I understand that this is very difficult. I can only offer an idea:
1. Atmospheric precipitation has a characteristic of X mm, similar to wind force.
2. Blocks have the parameter VOLUME (how much water it can absorb), HUMIDITY (the amount of water absorbed by the block) and POROSITY (how fast the water goes further down).
3. A block filled with water throws water to the side where there is less water (air, more porous blocks).
Thus, water will flow through the ravines. Like a river! If my PC does not explode at this moment . Prepared channels, carved out of stone, will direct water to reservoirs!
4. Depending on the biome, its dryness, it will be decided how much moisture the block loses per hour (probably too many calculations), per day.
5. Water goes down to sea level.
6. Rule - voids adjacent to the sea (ocean) are completely filled. Making channels for a sailboat will become more realistic!
Perhaps this will require a lot of computing power. But maybe we can run a series of simulations and get simplified rules for water processing.
In any case, this is an unprecedented gaming experience and a worthy challenge for the VS engine and the team!