system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does dishwasher rinse-aid work to make dishes drier and more sparkly?
gpt
Imagine a drop of water on a table.  Because of surface tension, it looks almost like a ball, right? The water all wants to stick together, rather than spreading out completely flat.

When that ball of water dries, any stuff that's not water (naturally occurring minerals and stuff) gets left behind.  And because the water was arriving together, the stuff gets left all in the same place.  That's a water spot.

Rinse aid is a surfactant, which reduces surface tension.  It makes the water less likely to stick to itself and more likely to spread out and flow down the drain.  That's why dishes get drier.  And the water that gets left to evaporate is less concentrated, so any stuff that gets left behind is thinner and more even.  Fewer water spots.