Eli5: How did native tribes drink from rives and streams without getting sick if they couldn’t boil the water?

Question

I know that the rives and streams had less man made pollutants, but what about parasites and such.

In: 4

Answer 1

We removed the forests and those forests were part of the natural filter system. Now we have crops everywhere that get tilled every year. This leads to agricultural runoff. These nutrients from the farms over-fertilize water bodies, basically making them cesspools for microbes. The Problem is, the biomass load is so high that the oxygen gets depleted. Dangerous microbes live in low oxygen conditions and these polluted waterways become a risk instead of a resource.

This pollution can be mitigated by 99% with one or both techniques names Keyline-Plowing, and or Permaculture-Swales. These landscaping techniques harvest water and stop erosion, turning the landscape into a natural filter again.