Interesting then what could be considered 3rd World...
[QUOTE=Tiradentes]Rio, just like most third world places, has a combined sewer system that collects both precipitation water and sewers together in the same conduits. During small rainfall events, the existing systems will convey the mixed fluids into a 'treatment' center before it gets dumped in the ocean. That's all good and dandy.[/QUOTE]This is the same type system the City of Atlanta has, except the overflow goes into the Chattahoochee River instead of the ocean.
As an observation from the late 90's, at the far end of Leblon beach is a "pumping facility" for the esgoto. As the local legend (knowledge) had it the effluent pipe went about a mile or so into the ocean and ended. The pipe broke somewhere much nearer the beach and the repair included an extension to about three miles or so into the ocean. Now I'm not aware of any sort of treatment plant anywhere in that area. I report, you decide. Also, the favelas of Vidigal and Rochina, the local lore is their effluent just drains right down the hill into. The ocean. Just an observation.