I get the sense people think we're cleaner than we really are. A great example are diseases like E. coli infections, campylobacter, hepatitis A, norovirus, cryptosporidium, etc. They are reasonably common and all are transmitted through the fecal-oral route. That is, the person getting sick ingested something contaminated with feces (human or animal).

Same thing with your own intestinal biome. You are sterile when you come out of your mother's womb. All of the bacteria that ends up in your intestine are ingested, often coming from your own family members.

Bacteria are everywhere. I'm not going to get overly worried about bacteria in the drinking water of planes unless it starts to make people sick.