What rain becomes once it hits the ground. The heaviest piece of the suite.
The vision
Weather stops when the drop lands. Water starts exactly there. Rain saturates the ground, percolates, swells the rivers, fills the hollows, and can end up drowning a cave or a cellar. Water gains a vertical axis it never had.
The module targets a real water engine: current of varying strength, overflow, drying, water bodies that are no longer infinite sources, and river dynamics.
Water is judged theoretically viable but mechanically hard, and a clear line emerges. Erosion, meaning terrain that transforms over time, is the real wall, perhaps impassable in a game where the ground is an array of blocks.
Everything else, simulated on fixed terrain, is far more reachable, almost simpler than weather. The roadmap reflects that: first a complete, playable water on fixed terrain, and only then, separately, the question of erosion.
Not all water is equal anymore. Running water and standing water are not drunk the same way, do not shelter the same species and do not irrigate a field to the same effect. The difference is visible before it is suffered.
In winter, water bodies freeze then thaw. A frozen river becomes a road, a frozen lake becomes a ceiling you can still fish under, and the landscape changes without a single terrain block moving.
Below ground, a table fed by seepage rises and falls with the seasons and the weather. Digging a well stops being decorative: it means reaching a dynamic resource, one that can run short.
On the surface, canals, dikes, drainage and irrigation let water be led across terrain that itself does not move. Enough to water a field, drain a hollow, or fill a moat in front of a monster nest.