When water runs down the drain or we flush it down the toilet, we usually don't care where it ends up. This is because with adequate basic sanitation, wastewater shouldn't be a concern. Yet, although humanity has already taken man to space and plans to colonize Mars, it continues to fail to provide basic living conditions for a large part of its population. A comprehensive study estimates that 48% of global wastewater production is released into the environment untreated. The UN, in turn, presents a much less encouraging figure, citing that 80% of the world's sewage is released without treatment. But returning to the question of the title, there are basically two destinations for sewage if it is not being released directly into the natural environment: it can be treated locally through septic tanks, or connected to a sewage treatment plant through the sewage network, eventually returning to nature after a series of treatment processes.
Sewage has been a problem for humanity since we first ceased to be nomadic and cities began to form. It is estimated that the first sewage installations appeared about 6,000 years ago, in Babylon. They used a simple ditch to concentrate the excrement. But soon even the Babylonians developed hydraulic systems to transport water through clay pipes. The history of sanitation systems is rich and, until the mid-20th century, sewage from virtually all urban centers was discharged untreated into a body of water, such as a stream, river, lake, bay, or ocean. That was the rule, not the exception. But this remains the reality for many, triggering huge public health problems. The issue is so critical that the Bill & Melinda Gates Foundation, a philanthropic institution, devotes much of its effort to “enable widespread use of sustainable and safely managed sanitation services that contribute to positive health outcomes, economy, and gender equality for the poorest people in the world.”
