re: question about bacteria in the waterways

Bacteria in the water is part of a natural and healthy ecosystem. However, the bugs that typically cause problems to human health are fecal coliforms.

They are usually found in high enough concentrations to cause infection as the result of poor sanitation.

There are other organisms in the water as well, and you may be somewhat right about hyper cleanliness leading to decreased resistance.

However as a society overall deaths from infectious diseases are very low compared to before the discovery of antimicrobial agents. Diarrheal diseases and wound infections were the number one killer. Now we die from diseases that typically pop up as you age like heart disease or cancer.