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London’s water supply and the introduction of sand filtration

London, United Kingdom




1 year




United Kingdom
Project achievements

Area improved

Local residents had access to safer drinking water

Economy boosted

By providing clean water, thousands of lives were saved, and London was able to grow

Solved the problem

Supply safe drinking water to Londoners

Develop a system of producing safe drinking water

Until the beginning of the 20th century, London’s water came from private companies, each supplying different areas of the capital.

One of the oldest of these firms was the Chelsea Waterworks Company. The business started trading in 1723, supplying much of central London with water.

The company converted two ponds into reservoirs in Green Park, near to where Buckingham Palace is now.

It built a third reservoir in Hyde Park about a mile to the north. Water came from the River Thames and was transported to the reservoirs using a series of small canals.

The Thames proved to be an unsustainable source of good drinking water. Increasing industrialisation in the late 18th and early 19th centuries saw the river become polluted as sewers and factories pumped a constant stream of waste into its waters.

Growing public criticism of the capital’s water companies came to a head in 1827 with a petition to parliament from campaigning politician Sir Francis Burdett.

Burdett’s petition claimed Thames water contained ‘the drainings from dunghills … the refuse of hospitals, slaughter houses [and] all sorts of decomposed animal and vegetable substances’. The petition went on to describe the water as ‘offensive and destructive to health’.

Chelsea Waterworks was the first company to react to the petition. The firm’s chief engineer James Simpson started experimenting with ways of purifying water. He completed a prototype sand filter bed at the company’s works by 1829.

The one-acre scheme was the first treated public water supply in the world. It was a major step forward in providing clean drinking water for large urban populations.

"The water taken from the River Thames at Chelsea, [is] offensive and destructive to health, [and] ought no longer to be taken up by any of the water companies from so foul a source”

FROM AN 1827 PETITION TO PARLIAMENT PRESENTED BY POLITICIAN SIR FRANCIS BURDETT Burdett Was Campaigning About The Poor State Of Drinking Water In London

London’s water supply and the introduction of sand filtration

Civil engineer, Jo Parker, talks to us about a development that made a dramatic impact on the health of London's population - slow sand filtration.

Did you know …

  1. Public water supply was only one of Sir Francis Burdett’s many interests as a reforming politician. He also championed prison reform and free speech.

  2. Burdett clashed with the House of Commons in 1810 when he protested against MPs sending the radical campaigner John Gale Jones to jail. Jones had criticised Parliament for holding debates in secret.

  3. MPs issued a warrant for Burdett’s arrest and he was thrown into the Tower of London. Released a few weeks later, he returned home along the Thames to avoid a public demonstration by his supporters.

Difference the project has made

James Simpson’s sand filter scheme provided filtered water for the residents of Chelsea. The method was quickly copied by other water companies.

As drinking water supplies became safer, water-borne diseases – such as cholera and typhoid – became less common. Thousands of lives were saved.

Reliable supplies of drinking water meant London could expand as a leading industrial city and global economic power.

How the work was done

James Simpson’s scheme used beds of loose brick, gravel and sand to purify river water. Ideas for the technique came from an experimental filtration unit set up at a Scottish bleaching factory in 1804.

Although sand filtration is slow, it’s reliable and it doesn’t use chemicals. Similar systems are still used in developing countries as they’re cheap and robust.

Sand filters work through the formation of a gelatinous layer – or biofilm - in the top few millimetres of a fine sand layer.

The biofilm builds up in the first few weeks of a scheme’s operation. It’s made up of bacteria, fungi and algae. The biofilm purifies the water – trapping particles of foreign matter and metabolising contaminants.

Water produced by modern sand filters can be of a high quality, with a bacterial cell count reduction of 90-99%.

People who made it happen

  • Designer and chief engineer: James Simpson (later President of ICE, from 1853 to 1855)

More about this project