The Sewers of London

There were many great works of spectacular engineering in the 19th century such as gigantic steamships, innovative bridges and fantastic buildings. None of them, however, saved as many lives as this immense and complex infrastructure project under the streets of one of the largest cities of the world: The Sewers of London.

It was 1854 and John Snow, a physician with his practice in the Soho part of London, poured over his map of the city. He'd been working on it since the first signs of a cholera outbreak that year. Carefully he had marked where each new case had appeared.

Seven Quick Facts
-Construction Dates: 1858 - 1870.
-Chief Engineer: Joseph Bazalgette.
-Size: 450 miles (720km) of main sewers fed by 13,000 miles (21,000km) of local sewers.
Made of: Brick and Portland Cement.
-Opening: Victoria Embankment July 25th, 1870.
-Operation: Drains depend mostly on gravity, with pumping stations at certain locations.
-Other: 318 million bricks were used in building the interceptor drains.

Cholera was the scourge of big cities in the 19th century and an outbreak could kill hundreds or thousands of people. The prevailing notion was that the infectious agent was carried through the air by smell, an idea called the "miasma theory." Snow suspected, however, that the disease was actually transmitted in some other way. In 1849 he'd written an essay, On the Mode of Communication of Cholera, suggesting that transmission was being made through unclean water.

His map seemed to bear out his idea. He found by looking at his records that all the recent cases clustered around a public water pump on Broad Street. Of those few cases that occurred nearer to another pump he found that the residents were still using the Broad Street pump anyway because they preferred the taste of the water. Especially telling was that of the 70 workers at a nearby brewery, none of them got sick. They only drank the beer provided to them for free. His study of the pattern of infection was so thorough that he managed to convince the local council to remove the handle from the pump, bringing the outbreak to a close.

Still, his ideas would not be generally accepted until after his death in 1858.

Fortunately, a project that would effectively solve the cholera problem in London was already underway by then, though the builders were mistaken in their beliefs about the source of the infection.

The Great Stink of 1858

Chief Engineer Joseph Bazalgette.

Plans for updating the London sewage system had been in the works for years, but it wasn't until the "Great Stink" of 1858, that politicians were spurred forward to find the money to put the project in motion.

Getting rid of raw sewage in a city as large as London had always been a problem. Originally, cesspools - stone-lined pits - had been used to contain human excrement. Often these were built right below the residence. As they filled up, these pits would have to be cleaned out every few years. As London grew to having nearly 200,000 cesspits, it started to be impossible to clean them all as often as they needed. Instead, they were eventually connected to London's existing sewers so that the effluent could be carried away that way.

These existing sewers, however, were storm drains not designed to handle human excrement. They were actually natural creeks and streams that had been covered over and thier contents deposited directly into the Thames River. The additon of sewage to these drains soon caused the shoreline of the river to be piled with untreated human waste and industrial effluent. When a severe heat wave hit the city in July and August of 1858, the smell from the river became unbearable. The stink, coupled with the idea that smell could carry infection, finally persuaded authorities to do something.

Civil engineer Joseph Bazalgette had been thinking about what to do about the London sewer system for many years. In 1849 he was hired by the Metropolitan Sewers Commission and one of his first jobs was to familiarize himself with the system. He realized it was a mess. There was no great plan or standardization to how the tunnels were built or connected. There was also no end of ideas on how to fix the system, but they were all expensive. Making things worse, the Commission was ensnarled in bureaucratic red tape and disagreements on how to proceed, so little progress was made.

British physician John Snow.

In 1856, however, The Metropolitan Board of Works took over for the Commission and promoted Bazalgette to chief engineer, giving him the responsibility to come up with a workable plan. His design was to create a set of massive drains that would intercept the existing sewers before they reached the river and carry sewage to a location east and outside of the city where it could be released safely downstream into the outgoing tide. These five tunnels, which were called "interceptor sewers," would be built along the path of the river, three to the north of the Thames and two on the south side. In some places where they ran along the river, these huge pipes would be hidden in massive embankments on either side of the waterway.

To make sure the material flowed through the drains easily Bazalgette decided the tunnels should fall at least two feet per every mile. Since the Thames only fell 3 inches per mile, this meant that pumping stations would have to be built at intervals along the path to raise the contents of the sewer so that the drains did not run under the level of the river.


It wasn't until 1858, when the horribly, odorous fumes began coming out of the river, that 3 million was authorized by Parliament to address the problem. The work started with the three northern sewers. The easiest way of building them was the "cut and cover" method. Workers would first dig a trench the width and depth of the tunnel and then the brickwork of the sewer would be built inside. To get the maximum strength, the drain was designed with an oval cross section similar to that of an egg. After the tunnel was finished, dirt would be used to cover it and make the ground level again.

Diagram showing the cross section of the tunnels.

Normally brickwork in such a tunnel in those days would be held together by using Roman cement. Bazalgette decided, however, to use a new material instead: Portland cement. It was a controversial choice, but he had concluded that it had superior strength and durability to Roman cement when it was submerged. He was proved right when an examination of the tunnels over a century later showed that the Portland cement was still holding the bricks firmly in position and did not need any repair.

Some of the considerations that made the construction project so complex was that there were already many tunnels and passageways under the City of London and Bazalgette's interceptor drains had to avoid them all while continuing their steady, downward flow. One of his biggest challenges came in 1865 when a drain had to cross the Metropolitan Underground Railway near Clerkenwell. This required that a one-hundred and fifty-foot-long underground aqueduct be constructed of wrought iron, just over the tracks. After it was complete, passengers on the trains rode along unaware that just over their heads was flowing as much as 60,000 gallons of sewage.

One of the most complex tasks of the project was building the pumping stations along the route. Bazalgette took the opportunity when he designed the pumping station at Abbey Mills to be able to finally show his work at an above ground location. As a result, the station is a testimonial to Victorian architecture.

By April of 1865, the first phase of the project was completed and a celebration was held at the Crossness pumping station to inaugurate the operation. The engines that drove the pumps were the largest in the world at the time, each weighing 240 tons and designed to lift the sewage 21 feet up. Like the Abbey Mills station, Crossness was a lot more attractive than one might think a sewage pumping station would need to be, showing an elegant Moorish architectural influence.

The Prince of Wales was the honored guest at the Crossness opening and under Bazalgette's direction, he turned the handle and started the massive beam engines running. During a speech that followed the Prince spoke saying that the project would allow everyone to look forward to the day "When London will have become one of the healthiest cities in Europe."

The Outbreak of 1866

The Abbey Mills pumping station. (Courtesy Gordon Joly licensed under the Creative Commons Attribution-Share Alike 2.5 Generic license).

There was at least one more major cholera outbreak before the system was completed. In July of 1866, a new epidemic occurred in the East End of London. William Farr, a statistician working with medical figures in England and Wales, investigated. Originally he had been a skeptic of John Snow's idea that cholera was transmitted by unclean water. As he gathered his data from this most recent outbreak, however, he changed his mind. The water delivered to sick households had all come through the East London Water Company. The company claimed that the water was filtered, but Farr had his doubts. His statistics indicated that only people being supplied by East London were getting sick. When Farr actually traveled to that part of the city and found some residences with eels in their water pipes, he had the proof that he needed that the company was not really filtering its water the way they said they were.

Farr's conclusions confirmed Snow's earlier work and soon it was accepted that the cholera was being transmitted through the water. With a firm knowledge of how the disease was spread, it was clear that the sewer system, coupled with clean sources of water, would bring the reign of this terrible illness to an end.


One of the last pieces of the new sewage system to be put in place was the Victoria Embankment which opened on July 25th of 1870. It was the culmination of the largest civil construction project in the world up to the time. To build the 450 miles (720km) of interceptor sewers, 318 million bricks were required and 876326.915 cubic yards (670,000cm) of concrete.

Though the Queen herself cancelled coming to the celebration at the last minute, she did knight Bazalgette for his work four years later.

John Snow, whose work was not appreciated in his lifetime, is now considered one of the founders of the modern science of epidemiology. A memorial, at the location of the deadly pump on what is now Broadwick Street, stands commemorating Snow and his work. The plaque shows a water pump with its handle removed.

Copyright Lee Krystek 2016. All Rights Reserved.