Blake_
Captain Obvious
Why complicate things to yet again burn my potatoe to a crisp? It can fill up only when it rains on the loaded chunk. Anything outside of it can be faked as a very slow average. Or it can fill up every time a player encounters rain on ANY chunk (actually it would store an amount but not actually write it until the player opens the item or exits the game), that would probably be better.Unloaded chunks and weather don't mix, so there is no current way to make it work with rain.
The hard way is to check weather on the chunk from the moment the item is placed. That could be hard on the system if many are placed and be a bother in terms of performance vs gameplay gains.