Flushing the Toilet: The "How" Behind Sewage Systems
- Kiran Koundinya Achyutuni
- Sep 23
- 3 min read
We all have toilets. But have you ever wondered where exactly they lead? It sounds hilarious, but the question really fascinates me. When did humans get creative enough to begin disposing of their fecal matter? It sounds like a basic question, but it explores the two-thousand-year-old science of sewage systems and the technological advancement that has led to our modern world of comfort. So let’s dive back into history and see how far we have come in dealing with our sewage.
Historical Sewage Systems
The first historical sewage systems popped up around 4000 B.C., around the time of the Babylonians. They engineered cesspits—a large hole in the ground where feces were collected—and used their knowledge of water flow to create a basic sewage pipe system where a few buckets of water could carry sewage far from a city.
The next advancement in sewage systems came around 3000 B.C. in the Indus Valley civilization of Mohenjo-Daro (located in present-day Pakistan), which designated buildings to act as latrines. These ancient public bathrooms were connected directly to the sewage system and were designed so that a few buckets of water could send the sewage into the Indus River.
The Romans expanded on the ideas of these basic sewage systems and evolved the latrine into something closer to a true toilet. Because of their developed sense of hygiene, the Romans also began distinguishing between wastewater and greywater, which increased their efficiency. Greywater is largely uncontaminated water, such as bath water, which was used to flush public latrines. The Roman jump in sanitary engineering is where we can begin to draw parallels to our modern systems today.
American Sewage Systems
The American sewage systems are divided into three categories: the wastewater system, the stormwater system, and the combined sewage system. These three types of sewers act independently to deal with human waste.
First, the wastewater system takes black water (water contaminated with feces or chemicals) and greywater through a household's sanitation pipes and transports them to a wastewater treatment facility. Ideally, this transportation would be done through gravity alone, but sewage must be pumped if it is to travel against gravity and go uphill. This is where manholes come into play and allow access to pumps such as grinder pumps or lift stations.
Second, stormwater systems do exactly as their name suggests: they take water from storms and funnel it through a separate system back into a nearby water source. Because most stormwater is clean, stormwater sewers must be completely separate from wastewater sewers to avoid contamination. You can probably find these sewers in your neighborhood. The next time you venture outside, look for a catch basin at the edge of the road; it should look like a hole at the edge of the sidewalk with a grate for protection.
Third, combined sewage systems take both wastewater and stormwater into the same sewer for disposal but are now very rarely used because stormwater would become contaminated when it could have been returned to a water source.
There you have it: a small explanation of our American sewage systems. It’s surprising to see how much work, thought, and learning goes into something as taken for granted as sewage systems. So the next time you find yourself contributing to your local sewage system, spare a thought for the work and effort it took to get humanity this far.
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