system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are the leaves of plants hanging down when they are low on water?
gpt
The leaves of plants have water inside of them that builds up a certain pressure. Imagine a balloon. If you blow air inside, the compressed air inside presses against the rubber of the balloon. If you find a balloon with air sideways, it stays horizontal. 

If the leaves don't have enough water, they are like an empty balloon that you hold sideways: because of the lack of pressure against the outer layer of the leaf it hangs down. 

If you water the plant, new “air” can enter in the balloon and it goes up again. 

I hope this helps :)