London sewer system

Year:1859

Duration:9 years

Cost:£3m (around £342m today)

Country: London, UK

What did this project achieve?

Create a sewerage system that channels it away from central London

By the 1850s there were 2.5 million people living in London. That meant 2.5 million people flushing their toilet waste into the city's storm sewers every day. From there it flowed straight into the river Thames.

The Thames was sluggish then. Instead of flowing down to the sea, the waste stayed put and the river became an open sewer.

People took their drinking water from the Thames so this meant water-borne diseases such as cholera spread easily. In 1853 a cholera epidemic killed 15,000 Londoners.

Despite much discussion nothing was done until 1858 when a hot summer made the Thames smell horribly. This became known as 'The Great Stink.'

As it was wrongly believed that cholera was spread through the air in a 'miasma' or smell. MPs' worries about their own health may have finally encouraged them to commission a new sewage system.

Civil engineer Joseph Bazalgette, who had just started as the chief engineer of London's Metropolitan Board of Works, was put in charge of the project.

Bazalgette's solution to the city's health problems was to build an extensive underground sewer network that diverted London's waste downstream to the Thames Estuary – away from the main areas where people lived.

Difference the sewers made (and continue to make)

The new sewer system eliminated cholera in London by removing contaminated water.

It also reduced the number of typhus and typhoid epidemics in the city.

How the work was done

Bazalgette spent 9 years digging up London to create 6 'interceptor' sewers, which were around 100 miles long altogether. Another 450 miles of sewer fed into them.

Some of London's 'lost' rivers were used for the network. These included the river Fleet, running under Fleet Street towards Covent Garden.

Building the interceptor system took 318 million bricks and 670,000m3 of concrete.

Bazalgette used Portland cement to build his sewers. Portland cement hardens as it reacts to water and it lasts a long time as a result. It's one of the reasons the tunnels are still in good order today.

The system included pumping stations at Deptford, Abbey Mills in the River Lea valley and on Chelsea Embankment.

While he was planning the system Bazalgette used the densest population in the capital, gave everyone the most generous allowance of sewage production and then came up with the diameter of pipe needed.

He then said, "We're only going to do this once and there's always the unforeseen" and doubled the diameter of the pipes he wanted built.

This foresight allowed for the increase in London's population that came years later with the introduction of the tower block. If Bazalgette had used the smaller pipe diameter, the city's sewers would have overflowed in the 1960s. Instead, they've coped into the 21st century.

“​‌

Joseph Bazalgette created a sewer system which he originally sized for London's needs of the time. He then doubled it to anticipate the future beyond. These are the qualities that I admire.

Sir Norman Foster

architect

Fascinating facts

Bazalgette's plans were similar to ideas suggested 25 years previously by the popular Romantic painter and illustrator John Martin.

Bazalgette had a close interest in every aspect of the work. Surviving records of the project are covered with thousands of his handwritten comments.

London's sewer network was named as one of the 'seven wonders of the industrial world' in a BBC TV series in 2003.

People who made it happen

  • Joseph Bazalgette, chief engineer of the Metropolitan Board of Works. Also president of the Institution of Civil Engineers from 1883.

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