system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: how come drinking cold water feels refreshing, but cold water on your skin is shocking like a cold shower?
gpt
Cold water in nature is *generally* cleaner (don't go out drinking water that happens to be cold, please), whereas tepid water has probably sat and may harbor dangerous microbes.  Drinking tepid or warm water is unpleasant, likely due to an evolutionary "memory" and preference for cool/cold water.

Conversely, there's never been an evolutionary advantage to jumping fully into cold water--probably a contraindication even.