

A lot of people don’t realize outside sewers and cities, septic systems are a thing and all the sewage goes to a tank that drains out into a patch of soil. A hundred feet/30 meters and usually even a wellhead is considered at a safe range.
Soils do a lot of biological treatment just as the enzymes and bacteria in septic tanks break down and dissolve solids.
UV disinfection and other treatment of sewage on-site is only common in areas with high water tables or proximity to waterbodies under that 100ft/30 meter range.
The majority of modern wastewater comes from other fixtures for laundry, showers, and the kitchen. Toilet sewage is relatively small volumewise.






A proper septic system is carefully engineered but they can still be quite low tech. Many houses still just have gravel trenches and pits.
My own home doesn’t have any pumps, it just pushes water out as water comes in. My tiny strip of land has deep trenches and the right native soil (deep sand).
More modern systems just need some pressurized lines and only three feet of the right sand to achieve proper treatment of effluents.