system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can animals drink water that sickens humans?

It seems every other animal can drink from any water source and be fine. Take watering holes in the desert for example - all kinds of animals gather to drink the dirty water. If humans drank it without boiling it first, we would become extremely ill. Was this always the case? When did humans become so susceptible to waterborne pathogens?
gpt
>It seems every other animal can drink from any water source and be fine.

Seems isn't *is.* 

Humans don't like to be sick with parasites and risk death from contaminated water sources.

Animals don't get a choice. 

They most certainly *do* get parasites and disease and can indeed die. 

Conversely, if you drink uncontaminated, but wild water, you won't get spontaneously ill. Those problems need to be present.