Things We Take for Granted: Clean Tap Water — From Cholera to the Kitchen Tap

Start hereIn 1854, within 250 yards of one London street corner, there were upwards of 500 fatal cholera attacks in ten days. The doctor John Snow linked them to a public pump. Why was water once so dangerous, and what changed?

Safe water from a tap is recent. In 1827, a petition called the Thames water supplied to part of London “offensive and destructive to health”. In 2024, about three in four people had safely managed drinking water at home, and one in four still did not. Here is how it changed, and one small way to use what you have.

011. Before: water that made people ill

In 1800s London, drinking water came from a polluted river and from street pumps. One of the city’s water companies, Chelsea Waterworks, took its water from the Thames.

In 1827 a petition to Parliament said the Thames water taken at Chelsea was “offensive and destructive to health”. It said the river carried “the drainings from dunghills” and “the refuse of hospitals”.

Water like that can carry disease. WHO lists diarrhoea, cholera, dysentery, typhoid and polio among the illnesses that contaminated drinking water can spread.

In the United States in 1900, diarrhoea and enteritis were among the three leading causes of death, with pneumonia and tuberculosis. Together with diphtheria, they caused one third of all deaths.

The Broad Street pump, 1854

In 1854, cholera killed hundreds of people around one London street in ten days. The doctor John Snow linked it to a public pump.

Within 250 yards of the spot where Cambridge Street joins Broad Street, near Golden Square, there were upwards of 500 fatal attacks of cholera in ten days. Snow found no particular rise in cholera in that part of London except among people in the habit of drinking from one pump-well. He put this to the parish’s Board of Guardians on the evening of 7 September, and the pump’s handle was removed the next day.

Snow added that the toll would have been much greater if so many people had not fled the area. He also compared the customers of two water companies. Our page on correlation and causation walks through his figures.

022. How it changed

Water got safer in steps: first filters, then chlorine, then national rules and a global target.

Sand filters

Running river water slowly through sand was one of the first big fixes. In practice, the water trickles down through the sand. A thin living layer near the top does the cleaning.

James Simpson, chief engineer of the Chelsea Waterworks Company, completed a prototype sand filter bed at the company’s works by 1829. It used beds of loose brick, gravel and sand. Sand filters work through a gelatinous layer, or biofilm, in the top few millimetres of fine sand.

Modern sand filters can cut the count of bacteria in water by 90 to 99%.

Chlorine

From the early 1900s, adding chlorine to kill germs, called chlorination, became normal practice.

Chlorination and other treatments of drinking water began in the early 1900s and became widespread, further cutting waterborne disease. In 1908 the Jersey City Water Works became the first system in the United States to practise large-scale chlorination on a permanent basis.

Chlorine left in the water can still act in the pipes, against germs that may get in through leaks and breaks. For example, it lets water treated at a plant miles away carry some protection on its way to you.

Rules and a right

Today WHO’s guidelines are a common basis for national drinking-water rules, and safe water is recognised as a human right. In practice, the rules that apply to your tap come from where you live. Some supplies, such as many private wells, sit outside them.

WHO’s drinking-water guidelines, in their 2022 edition, build on over 60 years of WHO guidance and have formed an authoritative basis for national regulations and standards. In 2010 the UN General Assembly explicitly recognised the human right to water and sanitation.

033. What the numbers say now

About three in four people had safely managed drinking water at home in 2024; one in four did not. Safely managed means water at home, free from contamination and there when you need it.

Between 2015 and 2024, coverage rose from 68% to 74%. In rural areas it rose from 50% to 60%, while in towns and cities it stayed level at 83%. So the share rose in the countryside and held level in towns and cities. Counted in people, though, three out of five who gained safely managed drinking water between 2000 and 2024 lived in towns and cities, because city populations grew so fast.

That still left 2.1 billion people without safely managed drinking water, including 106 million who drank directly from untreated surface sources. Surface water means lakes, ponds, rivers and streams.

In most countries with data, women and girls are mainly responsible for collecting water. Many in sub-Saharan Africa and Central and Southern Asia spend more than 30 minutes a day doing it.

Unsafe water is still estimated to kill hundreds of thousands of people a year. In its 2023 fact sheet, WHO estimates that microbiologically contaminated drinking water causes about 505,000 deaths from diarrhoea each year.

The world’s goal, UN target 6.1, is safe and affordable drinking water for all by 2030, tracked as safely managed water. WHO and UNICEF say universal coverage of safely managed services “appears increasingly out of reach”. At the current pace, their report projects 77% coverage by 2030.

044. Things people often repeat

Three popular ideas about clean water, and what the sources say.

“Taking the pump handle off ended the outbreak”

Partly The Broad Street outbreak ended because John Snow had the pump handle removed. The handle did come off, but Snow’s own count shows the outbreak was already fading. So the pump story fits Snow’s evidence about the cause, and is too neat about the ending.

How sure: Moderate it rests on Snow’s own day-by-day count of the outbreak, published the next year.

The most attacks in one day came on 1 September, at 143. On 8 September, the day the handle was removed, there were 12. Snow wrote that the attacks had so far diminished before the water was stopped that it was impossible to decide whether the well was still dangerous.

“Clean water was the main reason city deaths fell”

Still argued Clean water was the main reason deaths fell in early 1900s American cities. Both teams found that filtered water went with fewer deaths; they disagree on how much. For a reader, that shared finding is the safe takeaway.

How sure: Unsettled two teams studied early-1900s US city data and, after an exchange in one journal, still disagree on the size.

A 2005 study of major US cities credited clean water, meaning filtration and chlorination, with nearly half the fall in deaths. It credited clean water with three quarters of the fall in infant deaths. A 2022 reanalysis of 25 cities from 1900 to 1940 linked filtration to an 11 to 12% fall in infant deaths. None of the other measures it studied, including chlorination, sewage treatment and milk standards, appeared to have contributed to the declines. In a comment in the same journal, the 2005 authors corrected data mistakes and estimated that filtration explained 38% of the fall in total deaths in their sample. They called that result not very different from their original estimate of 43%. They added that the effects on infant deaths were smaller than in their original analysis.

A separate study of the Boston area, 1880 to 1920, credited clean water and sewers together with about a third of the drop in child mortality, by its measure. So the size of the effect is the open question, and so is the part played by chlorine.

“Safe water at home is normal everywhere now”

Doesn't hold up Almost everyone now has safe water at home. One person in four still lacks safely managed drinking water. That is real progress and a long way still to go.

How sure: Strong it is the official WHO and UNICEF global estimate, covering 2000 to 2024.

Between 2000 and 2024, about a quarter of the world’s population, 2.2 billion people, gained safely managed drinking water. The same report found 2.1 billion people still without it.

055. One small way to use it better

Find out where your water comes from and who checks it, by reading your supplier’s latest water quality report. For example, look up the river, lake or groundwater your tap draws on, and find it on a map.

In the United States, that report is called a Consumer Confidence Report. Community water systems must send their customers this annual drinking water quality report each year by July 1. It names the lake, river, aquifer or other source of the water and the regulated contaminants found in it. If you did not get one, you can call your water supplier or use EPA’s online search tool.

Private wells are different. EPA says private wells are not regulated by the federal government under the Safe Drinking Water Act, nor by most state governments. It says private well owners are responsible for delivering safe drinking water to their households.

In England and Wales, the Drinking Water Inspectorate has a map to find your local water company and the water quality in your area. If you are concerned about the quality of your drinking water, it says to contact your water company in the first instance.

Elsewhere, start with your water supplier or your local health authority. Our suggestion: the next time you fill a glass, remember that one person in four cannot yet do that safely at home.

06Quick answers

07Use this

08Quick quiz

How we checked this · Last checked October 2026

• We read John Snow's 1855 book in the Project Gutenberg text, and the WHO and UNICEF figures in their August 2025 report and news release.
• The CDC report dates from 1999. Its page blocks automated reading, so we checked it in the Internet Archive's copy.
• For how much clean water cut deaths, we read the abstracts of the 2005 study, the 2022 reanalysis and the exchange that followed, not the full papers.
• We left out EU water law because the official text site blocked our reader, and we would not quote it second-hand.
• Snow's comparison of two water companies is on our correlation and causation page, with its source.

How we check every article →

09Sources