In my experience, we use the 4 bucket system (Soapy initial scrub, soapy wash, river water rinse, and bleach river water disinfect) all done with river water and no alum. Have yet to get sick (knock on wood...) with lots of river days using this system.
Hand washing stations - wash the hands A LOT (before/after eating, groover, urinating, etc.), done with river water and soap, hand sanitizer finish
Sure, things can hide in the river water if you don't use enough bleach...