I know it's something different from what this mod adds currently but somehow in my mind this fits nice together. Puddles, like in this outdated forge mod. They would appear on solid blocks when it rains. You would be able to fill a glass bottle (this would play nicely with the Dehydration mod) from them and then a puddle would disappear. After rain and a few seconds/minutes they would vanish.

I really enjoyed this mod in the 1.12 days. Maybe I'll create this as a separate mod.
I'm gonna close this now, since it isn't really related to This Rocks.