They don't put sewer water back into municiple water where I live, but they do usually use it for irrigation or some other non-drinking use, where it will eventually evaporate which is the ultimate filtration because it will fall as rain and return to our natural water source, (groundwater).

Nah, thats not true at all.

Water that hits the sewer system goes through incredibly intense sanitation and filtering out of all the filth before going into the ocean as clean water, where it eventually evaporates and then rains back down into drinking catchments. Cycles round and round