Rainfall Should Fill Pits

In one of my bases, I hollowed it out all the way to the outer limits of the cube, and then constructed my home in the middle and placed a water dispenser on the wall. The result of this is creating a freshwater reservoir. It rains frequently, and my water dispenser is filling a wide square stone pit, which should naturally hold, and retain, water. It does, when the water dispenser is active, but the rainfall doesn't seem to accumulate, and it should, because it doesn't make sense that rain, especially heavy rain, falling into a solid stone basin, isn't steadily accumulating. It should accumulate even without a water dispenser, when conditions are set in such a way that it naturally and logically would.

The water and light mechanics in this game are spectacular, already, but I think this would add another little touch of realism for rainwater to accumulate in such a thing.