It was doctor John Snow, in London, who first proved a link between disease and water in 1854. He traced the outbreak of a disease called cholera and found that it was all connected to a single shallow well near the River Thames in London. When he stopped people from using the well, the disease went away.

Because the well was shallow, some sewage had seeped into it from pits nearby. People were drinking water filled with germs.

Once the link was understood, the government began to organise proper toilets connected to sewers. But early sewers still emptied directly into the rivers. It was only in 1858 – called “the Year of the Great Stink” – when the stench in the River Thames became so great that the politicians could not even stand to be in the Parliament building – that something was done.

During the second part of the 19th century, water in cities was at last purified and then piped to people. Most importantly, it was kept entirely separate from sewage. This was done by making all sewage water flow through pipes to a sewage treatment works where the germs were killed. This is the system we still use today.