The history
3,500 years from settling mud with alum to pushing water backwards through a plastic skin in millions of Indian kitchens.
For thousands of years people cleaned water by letting mud settle, boiling it and pouring it through cloth and sand. Then cholera showed that clear water could still kill, and cities turned to sand filters, chlorine and ultraviolet light. Meanwhile scientists discovered osmosis, and in 1959 and 1960 a UCLA team with an Indian-born chemist learned to run it in reverse. Today the same idea turns seawater into city water and hangs on kitchen walls across India, along with new questions about the water it wastes.
1748
Osmosis observed
Jean-Antoine Nollet, France
1829
Filtered water for a whole city
James Simpson, Chelsea Waterworks, London
1877
Osmotic pressure measured
Wilhelm Pfeffer, Germany
1908
Continuous chlorination of a US city's water
John Leal and George Fuller, Jersey City, USA
1910 (widely cited)
UV disinfection of a city's drinking water
Marseille, France
1959–1960
Practical reverse osmosis membrane
Sidney Loeb and Srinivasa Sourirajan, UCLA
1965
RO plant making drinking water for a town
Coalinga, California, USA
1981
Thin-film composite RO membrane patent
John Cadotte, FilmTec, USA
1984
Household water purifier brand in India
Aquaguard, Eureka Forbes
1500 BCE – 1800
No one knows about germs yet. People make water look and taste better by letting mud settle, boiling it, warming it in the sun and straining it through cloth, sand and gravel.
1500 BCE
c. 1500 BCE (reported)
The US EPA's history of water treatment says Egyptians reportedly used alum as early as 1500 BCE. Alum makes tiny floating specks clump together and sink, so clear water can be poured off the top. Tomb pictures from about the 15th to 13th centuries BCE show water being settled and siphoned.
Why it mattered. Clumping and settling dirt is still the first step at many water works today.
400 BCE
c. 400 BCE
The Greek doctor Hippocrates is said to have boiled water for his patients and then poured it through a cloth bag. The bag came to be called the Hippocratic sleeve. It caught the bits that made water cloudy and smelly.
Why it mattered. It is one of the earliest recorded water filters, a simple version of the first stage in a modern purifier.
300
c. 300 CE (older layers earlier)
This Sanskrit medical text advises boiling water, warming it in the sun and filtering it through sand and coarse gravel. Old books often say it dates from 2000 BCE, but scholars now think it was put together over several centuries and finished around the 3rd or 4th century CE. In India the seeds of the clearing-nut tree (nirmali or kataka) have long been rubbed in water pots to make mud settle.
Why it mattered. It shows people in India were already treating drinking water with heat, sunlight and sand, long before anyone knew about germs.
1748 – 1910
Scientists notice that water sneaks through thin skins towards salty or sugary liquid, and learn to measure how hard it pushes. They call it osmosis.
1748
Abbé Nollet tied a piece of pig's bladder over a jar of spirits of wine (alcohol) and sank it in water. After a few hours the bladder bulged outwards. When he pricked it, liquid squirted up more than a foot.
Why it mattered. It was the first recorded observation of osmosis: water moving through a thin skin towards the stronger solution.
1877
The botanist Wilhelm Pfeffer made a man-made membrane inside the wall of an unglazed clay pot. With sugar water inside and pure water outside, water flowed in and pushed up the pressure. He measured that pressure and found it grew with how much sugar there was.
Why it mattered. It was the first measurement of osmotic pressure, the push an RO purifier's pump must beat.
1886
1886 (Nobel Prize 1901)
Using Pfeffer's numbers, the Dutch chemist Jacobus van 't Hoff showed that dissolved substances push on a membrane much like a gas pushes on a container. The more stuff dissolved, and the warmer it is, the bigger the push. In 1901 he won the very first Nobel Prize in Chemistry, partly for this work.
Why it mattered. His law tells engineers how hard they must push salty water to force it backwards through a membrane.
1800 – 1920
Growing cities fight cholera and typhoid with sand filters, a map of a deadly pump, chlorine and the first ultraviolet lamps.
1829
The engineer James Simpson built slow sand filter beds for the Chelsea Waterworks Company. River water trickled slowly down through sand and gravel, which caught dirt and, as we now know, many germs.
Why it mattered. It is often called the first treated public water supply in the world.
1852
1852 (filtering required from 1855)
The Metropolis Water Act said that all of London's drinking water had to be effectually filtered from the end of 1855. Later laws added regular checks of what was in the water.
Why it mattered. It was one of the first laws anywhere to demand treated drinking water.
1854
When cholera killed hundreds of people in Soho, the doctor John Snow marked each death on a map. The deaths clustered around one water pump on Broad Street. He persuaded the local officials to take the pump's handle off.
Why it mattered. It helped prove that dirty water spreads disease, the reason we purify drinking water at all.
1877
Downes and Blunt left test tubes of a nutrient liquid in the sun and others in the shade. The ones in sunlight stayed free of microbes. The part of sunlight that did the killing turned out to be ultraviolet light.
Why it mattered. It is the discovery behind the UV lamp inside many home purifiers.
1887
c. 1887–1890
Ellen Swallow Richards, the first woman admitted to MIT, tested about 40,000 water samples for the Massachusetts Board of Health. She drew a 'normal chlorine' map showing how much salt the water naturally had in each place. Extra salt pointed to sewage pollution.
Why it mattered. Her work led to the first water-quality standards in the United States.
1908
26 September 1908
The doctor John Leal and the engineer George Fuller set up a plant that added chlorine to Jersey City's water at the Boonton Reservoir, every day, all the time. It treated about 40 million gallons a day. Within a few years chlorinated water spread across America and typhoid deaths fell.
Why it mattered. It was the first continuous chlorination of a US city's drinking water, one of the great public health wins in history.
1910
1910 (widely cited)
A few years after the mercury vapour lamp was invented, Marseille used ultraviolet lamps to disinfect city drinking water. It is widely cited as the first full-scale UV water treatment.
Why it mattered. It showed that light alone could make water safe, the same job the UV lamp does in a home purifier.
1950 – 1985
Chemists build plastic skins thin and tough enough to push water the wrong way, out of salty water. Reverse osmosis leaves the lab and starts making drinking water.
1959
Reid and Breton showed that thin films of cellulose acetate, a kind of plastic, let water through but held back most of the salt. The trouble was that water crept through far too slowly to be useful.
Why it mattered. It proved that a plastic skin could desalt water, if only it could be made faster.
1960
1959–1960 (patent granted 1964)
Loeb and the Indian-born chemist Srinivasa Sourirajan found a way to cast cellulose acetate so that it had a very thin, dense skin on top of a spongy support. Water flowed through far faster, and salt still stayed behind. Their patent was filed in 1960 and granted in 1964.
Why it mattered. This was the first practical reverse osmosis membrane, the ancestor of the one in every RO purifier.
1963
c. 1963
Engineers at General Atomics rolled flat sheets of membrane and spacer mesh around a central tube, like a Swiss roll. Water pushed in along the outside and clean water spiralled into the tube.
Why it mattered. The spiral-wound element packs a large membrane into a small tube, and it is the shape of the RO cartridge in a home purifier.
1965
June 1965
Coalinga's well water was too full of minerals to drink, so drinking water was brought in by railway tank cars. A small plant with Loeb's membranes began turning the salty well water into drinking water, about 5,000 gallons a day.
Why it mattered. It was the first reverse osmosis plant to make drinking water for a town.
1981
filed 1979, granted 7 July 1981
John Cadotte made a new kind of membrane by letting two chemicals meet where water and oil touch. They react into a polyamide layer far thinner than a hair, right on top of a porous support. His patent reported over 99.3% salt rejection with high flow.
Why it mattered. Almost every RO membrane made today, at home or in giant plants, is a thin-film composite like his.
1984 – today
In India, UV and then RO purifiers become ordinary kitchen appliances. Standards and courts start asking how much water they waste and when they are really needed.
1984
Eureka Forbes, a joint venture of Forbes & Company and Electrolux, launched its Aquaguard water purifiers. Families who had only boiled or cloth-filtered water now had a machine on the wall that filtered it and killed germs with ultraviolet light. Aquaguard became so common that many people use the name for any purifier.
Why it mattered. It created the home water purifier market in India.
1984
The World Health Organization published the first edition of its Guidelines for Drinking-water Quality. They give countries a science-based list of what can safely be in drinking water, from germs to chemicals.
Why it mattered. Many national standards, including India's, lean on these guidelines.
1999
March 1999
Mahesh Gupta, an engineer who studied at IIT Kanpur, started KENT RO Systems after his own children fell ill from contaminated water, according to the company. KENT sold home purifiers that used reverse osmosis, a technology then mostly found in factories and plants.
Why it mattered. Home RO purifiers spread fast in Indian cities where groundwater is hard or salty.
2012
2012 (first issued in the 1980s)
The latest version of IS 10500, India's drinking water specification, says the acceptable level of total dissolved solids (TDS) is 500 mg per litre. Up to 2,000 mg per litre is permitted when there is no better source.
Why it mattered. This 500 mg per litre line is the number most Indian arguments about RO come back to.
2015
2015 (updated 2023)
BIS published IS 16240, the Indian Standard for reverse osmosis purifiers used at home. Purifiers certified under it are tested for things such as how well they clean water and how much of the input water they recover.
Why it mattered. It gave buyers a way to trust a purifier, and put water wastage into the rulebook.
2019
May 2019
India's National Green Tribunal told the government to stop RO use where water already has less than 500 mg per litre of TDS. It asked that purifiers recover more than 60% of the water, aiming for 75%, and that the reject water be used for mopping, gardening or washing. A 2020 draft rule, later tribunal orders and a 2022 Supreme Court stay kept the debate going.
Why it mattered. It made the whole country ask how much water home purifiers throw away, and whether soft water really needs RO.
2000 – today
Giant RO plants turn seawater into drinking water for millions, using far less energy than the first plants, but leaving salty brine behind.
2010
July 2010
The Minjur plant began turning seawater from the Bay of Bengal into 100 million litres of drinking water a day by reverse osmosis. A second 100 million litre plant at Nemmeli began in 2013. A much bigger 400 million litre plant at Perur is expected around 2027.
Why it mattered. Minjur was India's largest desalination plant when it opened, and it made seawater a real water source for an Indian city.
2013
October 2013
The Sorek plant opened with a capacity of 624,000 cubic metres of drinking water a day, making it the world's biggest seawater RO plant at the time. It stacks huge 16-inch membrane tubes upright to save space.
Why it mattered. It showed seawater RO could supply a large share of a whole country's tap water.
2019
A study counted 15,906 working desalination plants making about 95 million cubic metres of fresh water a day, almost half of it in the Middle East and North Africa. It also found they make about 142 million cubic metres of salty brine a day.
Why it mattered. It showed that the waste stream, not just the clean water, is a big part of the desalination story.
By the numbers
Better membranes and devices that recycle pressure cut the electricity needed for each cubic metre (1,000 litres) of fresh water from the sea. Physics sets a floor of about 1 kWh per m³.
Did you know?
Sidney Loeb earned about $14,000 from the RO patent over its whole life, for an invention that grew into a multi-billion dollar industry.
Many older home RO purifiers kept only about 1 litre in 5 of the water that went in; the rest went down the drain as reject water.
Desalination plants around the world make more salty brine each day, about 142 million cubic metres, than fresh water, about 95 million.
Pulling the salt out of seawater needs at least about 1 kWh per cubic metre, a limit set by physics, and the best plants now use less than twice that.
When Nollet pricked his bulging pig's bladder in 1748, the liquid squirted up more than a foot.
The people
1700 – 1770 · Physicist and priest · France
The first person known to record osmosis, using a pig's bladder and a jar of alcohol.
1845 – 1920 · Botanist · Germany
Built a membrane inside a clay pot and measured osmotic pressure for the first time.
1852 – 1911 · Chemist · Netherlands
Wrote the law of osmotic pressure and won the first Nobel Prize in Chemistry.
1813 – 1858 · Doctor · England
Mapped cholera deaths around the Broad Street pump and showed disease could spread through water.
1842 – 1911 · Chemist · USA
The first woman at MIT, whose huge water survey led to America's first water-quality standards.
1858 – 1914 · Doctor and health officer · USA
Put chlorine into a US city's water every day, starting in Jersey City in 1908.
1917 – 2008 · Chemical engineer · USA and Israel
Co-invented the first practical RO membrane, then moved to Israel and invented pressure retarded osmosis.
1923 – 2022 · Chemist and chemical engineer · India and Canada
Born in Tamil Nadu, he co-invented the RO membrane at UCLA and later made Canada's National Research Council a world centre for membrane research.
Where it happened
Sources
Dates marked “c.” are approximate, and historians sometimes disagree about who was first. If you spot a mistake, tell us.
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