system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5: Why are tears, sweat, and nasal (whatever the right term is) salty? What is the purpose and function?
gpt
The saltiness is how the body extrudes the water. Cells can't actively move water by themselves - they have to kind of *persuade* the water to move by itself. Water loves salt. But water is also socialist - it spreads out by itself so that every water molecule gets the same level of access to salt. So, when a cell wants water to move somewhere, it has to bait it. The cell picks up some of the salt it has inside itself and pushes it out into the sweat gland. Then, the water notices that there's less salt inside the cell but lots of unclaimed salt *outside* the cell, so a big horde of socialist water zombies charge out of the cell and hang out in the sweat gland with all the salt - enough socialist water zombies until each socialist water zombie both inside and outside the cell has equal access to salt. 

Now of course, this is all just a clever ruse by the cell - once the water is outside the body, the sun's energy is free to evaporate it. Most of the water will do this, leaving just a kind of sticky, salty sheen on the skin.