when water becomes unsafe because of harmful bacteria, how does that spread?

Question: when water becomes unsafe because of harmful bacteria, how does that spread?
- Keywords:
  bacteria,
  contamination,
  water
Asked by Anita xx on 18 Jun 2025.
- Samuel Bloomfield answered on 18 Jun 2025:
  
  Harmful bacteria in water often originate from human waste or farm run-off (water that flows over farms and picks up animal waste). These bacteria reach rivers and streams that flow into each other. Humans that swim or play in the water can then be exposed to these harmful bacteria.

Question: when water becomes unsafe because of harmful bacteria, how does that spread?