I know this probably sounds hypochondriac, but seriously - I learned that some people do shower enemas i.e. taking off the shower head, insert the hose in their anus, and run water. THAT IS SO GROSS if they decide to do that with a shower that other people will use later, e.g. at hotels.
If the worst thing you can catch from using the water source contaminated by these people's various bodily fluids + solids is 1 day of vomiting and diarrhea, it would not be that big of a deal, but can you catch more serious diseases like hepatitis or parasites? Then is there an effective way to disinfect inside the holes of shower and tap water?