Wandsworth Western Riverside Waste Authority & River Wandle

The Thames is a tidal river with “brackish” water—a mix of fresh and saltwater. While drinking from the Thames is unsafe, it has historically been used for various domestic and industrial purposes like cooking, brewing, and power generation.

In medieval London, people accessed drinking water from tributaries or communal wells and pumps connected to underground springs. By the 13th century, there were already complaints about dirty water supplies, prompting the City of London to build its first organized water system—a large pipe known as the Great Conduit. Completed in 1245, this 2.7-mile-long conduit brought fresh water from a spring near modern-day Marble Arch into the city.

The water flowed via gravity to a column-shaped building where people could fill their containers. Conduits became local landmarks and, on special occasions, even dispensed wine! As the city grew, more conduits were built. This network supplied London until the Great Fire of 1666 destroyed it.

In 1582, a Dutch engineer named Peter Morice revolutionized London’s water supply by installing waterwheels and pumps at London Bridge. This system, which could pump over four million gallons a day, was the first to overcome the limitations of gravity alone and remained in use until the early 1800s.

Another water project, the “New River,” was initiated in 1609 by Sir Hugh Myddleton. This canal brought water from Hertfordshire to London and still supplies some of the city’s drinking water today. However, by 1800, half of London’s water supply, including drinking water, came directly from the Thames, thanks to new technologies like steam-powered pumps.

But as London expanded, so did its waste problem. Without a proper sewage system, waste flowed into the streets and rivers. The River Fleet, once compared to Venice’s canals, turned into a filthy ditch filled with garbage. The Thames, once a thriving habitat for fish like salmon and eels, became increasingly polluted. By 1857, a Natural History Museum study found no fish between Kew and Gravesend.

The situation reached a crisis point during the “Great Stink” of 1858. A scorching summer made the smell of the sewage-filled Thames unbearable. Even Queen Victoria complained about the stench after a visit to the SS Great Eastern. This prompted Parliament to pass the Thames Purification Bill in 18 days, giving the Metropolitan Board of Works the power to tackle the problem.

Joseph Bazalgette, the chief engineer, designed an ambitious sewer system to divert waste away from London. Completed in 1875, it featured 82 miles of underground sewers and pumping stations, still in use today. However, the system only moved the problem downstream. In 1878, the passenger steamer Princess Alice sank near the sewage outflow, leading to many deaths from ingesting the polluted water. This tragedy led to using “Bovril boats,” which carried sewage to the Thames Estuary until 1998 when the EU banned the practice due to beach contamination.

Despite these issues, London’s drinking water had been separated from the tidal Thames since 1852, improving overall water quality. The Metropolis Water Act mandated that water companies find sources upriver and filter the water through slow sand filters. These simple but effective filters, still used today, consist of sand, gravel, and brick layers topped with a bacteria layer that cleans the water as it passes through.

The Metropolitan Water Board, established in 1902, coordinated efforts to improve water quality and implement new technologies. After World War II, bomb damage and suburban expansion again worsened water quality, and by the 1960s, the Thames was biologically “dead.”

Efforts to improve the river resumed, and today, while sewage still occasionally (perhaps not so “occasionally”) overflows into the Thames, conditions are much better. The Thames Tideway Tunnel, currently under construction, aims to capture sewage overflow and redirect it to treatment plants. Scheduled for completion in 2025, this £4.2 billion project will further improve water quality and support aquatic life.

While there’s still work to be done, the river is in far better shape than during the dark days of the Great Stink.