In ancient times, when the population of the Earth was at a much lower level, human waste could be disposed of by throwing it into a river, using it for fertilizer, or the still popular camping method of burying it.
While ancient Rome invented an early version of sewer systems that involved moving water through underground channels, its primary purpose was more of a storm drain than a hygienic sewer.
Human waste was often still just dumped into the street.
The cesspit was an early attempt at containing such organic matter.
Cesspits are ditches dug into the basements of or spaces between houses. The brick-lined caverns were used to receive and contain waste, either from privies connected to the cesspit via a channel, or simply from tossing your family’s bucket-o-gunk into the neighborhood’s slop trough.
Often lined with brick or stone, the pits were intentionally porous so that liquid could filter through the ground and leave more room for solid waste.
And in case you were wondering, they were called “nightmen” because that’s the only time they were allowed to do their…business.
The reduce, recycle, reuse spirit of cesspits was noble, though no doubt stinky, and worked fairly well as a system…until populations began to grow.
During industrialization, the mass migration of people from the countryside into cities such as London outpaced the capacity of cesspits.
Crowded slums and overflowing cesspits were a recipe for infectious disease, and London had its first cholera outbreak in 1831.
If you thought the idea of regular sewage in the street was gross, let me tell you, cholera sewage is worse.
Cholera is caused by bacteria and is spread through what’s known as fecal-oral transmission.
This means the waste from people infected with cholera contaminates the water or food that other people eat or drink, and then those people get infected.
If left untreated—which it was in the 1800s, because treatment didn’t exist—it can kill within hours of symptoms starting.
You know what’s a really bad disease to have to deal with when you don’t have a proper way to handle sewage? One that’s spread through sewage.
The government of London realized there was an issue and put a man by the name of Edwin Chadwick on the case.
He was able to determine that there’s a link between poor living conditions and disease.
Chadwick decided the move was to remove waste quickly, which is a good idea in theory. The problem is that Chadwick believed in what was known as miasma, a popular idea at the time that illness was the result of “bad air” (this was an era before germ theory, when we learned that microscopic bacteria made you ill, not just smell).
As a result, he thought the smell of the waste was the problem, and that it could be solved by moving more waste out of the city and into the River Thames…which is where most Londoners got their drinking water.
Needless to say, there were more cholera outbreaks.
One of the most notable cholera outbreaks happened in 1854.
In a period of about 11 days, spanning late August to early September of 1854, over 500 people died in the area around Broad Street in the Soho neighborhood of London.
John Snow, a doctor, already held some suspicions that cholera was transmitted by water, not by air, and saw the outbreak as an opportunity to prove his theory.
His data collection relating to cholera deaths in the area showed they were all clustered around a particular water pump on Broad Street.
His evidence was strengthened by the fact that two ladies in Hampstead, an area several miles from Broad Street, had also died of cholera. Upon further investigation of the deaths, Snow learned that the madam of the house had a bottle of water from the Broad Street pump delivered to her daily, as she preferred the taste.
Snow convinced local authorities to remove the handle of the Broad Street pump, which was largely a symbolic gesture as the outbreak had already run through all available victims and was declining.
Despite a solid body of evidence, others weren’t ready to accept the theory of cholera as a waterborne illness…
By summer of 1858, the idea that dirty water could make you sick still hadn’t caught on, but the smell of the Thames, which was basically an open air sewer at this point, was enough to finally inspire the city of London to clean up their act...literally.
The time is, less than affectionately, known as The Great Stink.
While, like Edwin Chadwick, their theory on the cause of illness was wrong (everyone was operating under the assumption that the foul stench of human waste was creating miasma that was causing disease), the solution was better than what old Chadwick had tried.
A massive undertaking of new, larger, sewer systems was created that took waste further down the Thames so it could be washed out to sea.
In turn-of-the-century Chicago, they had a similar problem.
They’d already built their sewer systems, but they’d built them to dump into the Chicago River, which then flowed into Lake Michigan, which is where Chicago got its drinking water.
With no nearby ocean to extend their pipes to, they did the next most obvious and reasonable thing: They reversed the flow of the Chicago River, so instead of it pushing river sewage out into Lake Michigan, it would flow into the Mississippi, taking a tour of America, and out into the Gulf.
It was an extreme engineering project that, while it did clean up the river, made no friends of their southern neighbors.
Most modern sewers divert waste to treatment plants that can filter out solids and disinfect the remaining water using chlorine, ultraviolet light, or ozone, before releasing it back into the larger systems.
There’s all kinds of gross stuff that can be transmitted when people are leaving their feces willy-nilly.
In addition to cholera, contaminated water can also aid the spread of other bacteria such as E. coli, salmonella, and shigella.
It can also spread viruses like norovirus, rotavirus, hepatitis A, and polio, as well as parasites such as cryptosporidium, giardia, and amoebas.
Did you know, in addition to giving everyone nightmares about brain eating amoebas, amoebas can also cause their own form of dysentery?
Typhoid fever, made famous by the legendary Typhoid Mary, ravaged major cities before the improvement of water sanitation.
In Chicago in 1891, it killed upwards of 1,700 people.
In Pittsburgh in the early 1900s, the introduction of filtrations and chlorination to wastewater caused the death rate of typhoid fever to drop by about 85%.
Unfortunately today, the World Health Organization estimates that over 5 billion people worldwide don’t have access to basic sanitation services like private toilets and latrines, and 40% of household wastewater is discharged without treatment.
This contributes to diarrheal diseases being the third leading cause of death in kids under 5 years old.
So, you should certainly thank your modern sewer system for protecting you from all of that, but did you know that sewers continue to be the gift that keeps on giving?
Sewers are increasingly being viewed not just as a means to remove potentially harmful pathogens, but also as a way to collect them…or rather, collect data about them.
Researchers have increasingly begun using what’s known as “wastewater surveillance” to study pathogens circulating in a community.
By collecting samples from existing sewer systems and centralized treatment plants, we can test waste for the presence of new diseases or track changes in levels of commonly circulating disease.
This data can then be used to get a sense of disease burden within a large community, or in a more localized area, depending on where samples are collected.
You can use wastewater data to tell if an entire city is experiencing higher than average levels of disease, or if an outbreak is localized to one neighborhood, allowing health workers to better focus their outreach.
A lot of people have become more familiar with wastewater surveillance as a result of the COVID pandemic.
At a time when many people have the ease and comfort of testing at home, it’s been increasingly difficult to get an accurate sense of cases in the community.
By testing wastewater, we’re able to approximate levels of COVID in an area without needing to rely on reported tests.
And COVID isn’t the only disease that this sort of surveillance works on. Polio is another highly contagious waterborne illness that’s often carried with no symptoms.
Detecting polio virus in wastewater can alert health departments to the potential for an outbreak before it happens, spurring them into action to increase vaccination coverage in the area when necessary.
During the mpox outbreak in 2022-2023, wastewater was used to test how accurately it could detect the presence of mpox in a community.
In a time of limited public health resources, being able to determine if a pathogen is present or not amongst thousands to millions of people without having to test each person could be essential to preventing an epidemic.
The possible future applications for wastewater surveillance are exciting as well (I mean I assume you all are excited about sewers by now).
Imagine being able to detect the rise in resistance to certain antibiotics through sewers and not through outbreaks of untreatable diseases.
Or testing the wastewater storage on airplanes to detect new viruses or bacteria entering a country before it’s widespread in people.
