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.



Civil engineer, Jo Parker MBE, talks about a development that made a dramatic impact on the health of London’s population – slow sand filtration:

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%.