system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5: how do those water dispensers heat and cool water so quickly?

Like those water dispensers that have the hot and cold water. How does the hot one produce near boiling water and the cold one  really cold water directly after one another?
gpt
There is a small holding reservoir for each side, that is heated or chilled. It is not an infinite supply, and you will eventually run out after filling multiple water bottles, and would eventually get room temperature water.