In many parts of London the sewers still date from the Victorian era. And whilst many are still in a good state of repair and need little work to bring them up to current standards, it’s unfortunate that over time these sewers do silt up and the volume of waste they can handle decreases.

Londoners owe a lot to the Victorians, who revolutionised sanitation in the capital. In the 1850s around 400,000 tonnes of raw sewage were disposed of in the River Thames every day of the year, effectively ending the River’s life.

The engineer Sir Joseph Bazalgette was tasked with bringing the sanitation system into the 20th century and was given £3m to build a network of interconnecting sewers, treatment works and pumping stations across the capital. The system was capable of coping with the sewage from around 2.5 million residents, a figure which has long since been eclipsed.

The original sewer design collected both rainwater and sewage in the same sewer pipes. This meant that at times of heavy rainfall, the sewers would overflow. He thus designed sewer overflows into the Thames where this sewage could be disposed of.

Thames Water is currently in the process of a £675 million pound scheme to upgrade five principal sewer systems, and have started work on the Lee Tunnel which is expected to deal with the largest combined sewer overflow point. They are also in negotiations to build the Thames Tunnel, a sewer which will stop waste entering the River Thames through 34 sewer overflows along the length of the river.

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