Without domesticated animals, or industry, there are very few pollutants in the water. Fresh water from mountain streams etc. Is normally safe to drink. Unfortunately man has caused the majority of the pollutants in the water.
How did man survive before they found fire? Boiling water sanitises it, but how did man not die before leaning this?
A) not for very long in most cases. 20-25 years was the typical life expectancy. Early humans died from the simplest afflictions, often from loss of teeth resulting in starvation.
B) Luck and observation.
They survived just like wild animals survive today. They tell you not to drink the water in some foreign countries because there is bacteria in it. People build immunities to the local bacteria. I am sure water was low on the list of things that killed early man. Exposure, poor diet, and injuries were more likely to kill them.
Human's didn't die, they had watching them friends.
Still do.
