Flush toilet

• 1. Introduction

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  The flush toilet is one of the most quietly consequential inventions in human history, and yet most people give it almost no thought at all. At the Great Exhibition in Hyde Park in 1851, 827,280 visitors paid one penny each to use a novelty called the Monkey Closet. For that penny they received a clean seat, a towel, a comb, and a shoe shine. The phrase "to spend a penny" entered the English language as a euphemism for visiting the toilet. That single detail captures something important: for most of human history, answering nature's call was a matter of public negotiation, seasonal inconvenience, or outright hazard. The flush toilet changed all of that. What allowed a device built around water and ceramic to become indispensable? Who actually built it, and how has it kept evolving? And why does the direction water swirls when it flushes have nothing to do with which side of the equator you live on?

• 2. Ancient Foundations

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  Around 4000 BCE, the Mesopotamians introduced clay sewer pipes to the world. The earliest known examples appear at the Temple of Bel at Nippur and at Eshnunna, where they carried away wastewater and captured rainwater in wells. The city of Uruk goes even further back. Both squat and pedestal latrines built from brick have been found there dating to 3200 BCE, making them among the earliest known purpose-built toilet structures anywhere.

  The Indus Civilization, the Egyptians, and the Minoan civilization all constructed flushed toilet systems of their own. The Minoans, by the second millennium BC, had developed flushable pedestal toilets. Excavations at Knossos and Akrotiri have turned up examples. Further north, the oldest Neolithic village in Britain, Skara Brae in Orkney, dating from around the 31st century BC, used a stream and a connecting drainage system to wash waste away.

  The Romans built communal latrines across their empire from the first through fifth centuries AD, feeding waste into primary or secondary sewers. A well-preserved set of these latrines survives at Housesteads on Hadrian's Wall in Britain. They did not flush in the modern sense; a continuous stream of running water did the work. When the Western Roman Empire fell, these systems fell out of use in Western Europe, though the Eastern Byzantine Roman Empire kept repairing toilet pipes and sewers for centuries afterward.

  In February 2023, archaeologists in China announced what may be the world's oldest known flush toilet proper: a 2,400-year-old lavatory unearthed at the Yueyang archaeological site near Xi'an. Researchers from the Chinese Academy of Social Sciences' Institute of Archaeology found broken parts of the lavatory and a bent flush pipe among the ruins of an ancient palace.

• 3. Inventors and Patents

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  In 1596, Sir John Harington published A New Discourse of a Stale Subject, Called the Metamorphosis of Ajax. The book described a forerunner to the modern flush toilet that he had installed at his house at Kelston in Somerset. It had a flush valve to release water from a tank and a wash-down design to empty the bowl. Harington went on to install one for his godmother, Queen Elizabeth I, at Richmond Palace.

  The S-trap, still found in toilets today, was invented in 1775 by the Scottish mechanic Alexander Cumming. His device used standing water to seal the bowl's outlet, blocking foul air from rising up out of the sewer. Two years later, Samuel Prosser applied for a British patent for a "plunger closet".

  Joseph Bramah came to toilets by accident. He began his professional career installing water closets based on Cumming's 1775 design, and he noticed that the models being fitted in London houses had a tendency to freeze in cold weather. Working with a collaborator named Allen, he replaced the usual slide valve with a hinged flap that sealed the bottom of the bowl. He also devised a float valve system for the flush tank, patented in 1778, and set up a workshop in Denmark Street, St Giles, where he manufactured what was arguably the first practical non-manual flush toilet. Production continued well into the 19th century, with the design used mainly on boats.

  The washout toilet, a flat-platform design with a shallow pool of water, was patented in Britain by George Jennings in 1852. That same type had already been the standard toilet in Britain throughout the 19th century. On the mechanical side, Albert Giblin designed the siphon discharge system that Thomas Crapper would later manufacture and popularize. Giblin received a British patent for what he called the "Silent Valveless Water Waste Preventer". Crapper, despite a persistent popular legend, did not invent the flush toilet. He did hold nine patents, three of them for water closet improvements, and in 1880 he introduced the U-shaped trap.

• 4. Victorian Industrial Growth

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  George Jennings set up his business manufacturing water closets and sanitary pipes at Parkstone Pottery in the 1840s. It was Jennings who brought the flush toilet to a middle-class audience. At the Great Exhibition at Hyde Park, which ran from the 1st of May to the 15th of October 1851, his Monkey Closets drew enormous public interest and the toilets at Sydenham that followed went on to earn more than £1,000 per year. He opened the first underground public convenience at the Royal Exchange in 1854.

  Thomas William Twyford pushed the technology in a different direction. He invented the single-piece ceramic flush toilet, an innovation that would define the fixture's appearance for more than a century. In 1875 the "wash-out" trap water closet entered the market and quickly became the public's preferred basin type. By 1879 Twyford had created his own version, which he named the "National", and it became the most popular wash-out water closet of its era. By the 1880s his "Unitas" model, free-standing and made entirely of earthenware, had arrived on the market. Its free-standing design made cleaning easier, which made it more hygienic. In 1888 Twyford applied for patent protection for his "after flush" chamber, a device that refilled the basin with a lower quantity of clean water after flushing.

  The modern pedestal "flush-down" toilet was demonstrated by Frederick Humpherson of the Beaufort Works in Chelsea in 1885. By the end of the 1850s, building codes already suggested that most new middle-class homes in British cities should be equipped with a water closet. The Public Health Act 1875 laid down stringent requirements for sewers, drains, water supply, and toilets, giving official weight to the growing sanitary movement. The leading manufacturers issued catalogues, opened showrooms in department stores, and sold their products internationally. Twyford maintained showrooms in Berlin, Sydney, and Cape Town.

• 5. The Flushometer and Beyond

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  In 1906, William Sloan first made available his "flushometer" style toilet flush valve, a design incorporating his patented mechanism that connected directly to the pressurized water supply rather than using a holding tank. The design proved efficient and popular; flushometer valves remain a standard fitting in commercial restrooms worldwide. One year later, Thomas MacAvity Stewart of Saint John, New Brunswick, invented the vortex-flushing toilet bowl, which created a self-cleansing effect inside the bowl. Philip Haas of Dayton, Ohio, made further refinements, including the flush rim toilet with multiple jets of water from a ring.

  The spread of flush toilets beyond Britain was rapid. An early benchmark on the European continent was the three "waterclosets" installed in the town house of banker Nicolay August Andresen at 6 Kirkegaten in Christiania, insured in January 1859. The insurance ledger used the English term "waterclosets", an indication that the units were most likely imported from Britain. In 1860, a flush toilet was imported from Britain for Queen Victoria's rooms at Ehrenburg Palace in Coburg, Germany, with the stipulation that she alone could use it. Flush toilets reached Batavia in the Dutch East Indies by 1872.

  In Australia, the company Caroma developed the Duoset cistern in 1980: a single unit with two buttons and two flush volumes as a water-saving measure. Modern versions of the Duoset are now sold worldwide. The company found that modern dual-flush designs save the average household 67% of the water used by conventional single-flush units.

• 6. Mechanical Choices

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  The tank fill valve, found in every tank-style toilet, comes in two main designs: the side-float type and the concentric-float type. The side-float design has existed for over a hundred years; the concentric design has only been around since 1957. The concentric float's more compact layout reduces interference with the flapper valve and tank insulation, and it has a practical safety advantage: when a slow leak develops, it makes considerably more noise than the older side-float design, which tends to be nearly silent even as water drips away.

  Between the flapper-flush valve, common in North American and continental European homes, and the siphon system, which was mandatory in the UK until the 1st of January 2001, there is a meaningful engineering tradeoff. The flapper valve is easier to operate but almost inevitably starts to leak after a couple of years of use as particles wear the valve seat. Research in the UK found that between 5 and 8% of toilets, most of them dual-flush drop valves, are leaking, each one losing between 215 and 400 litres on average per day. The siphon system, invented by Albert Giblin, has no sealing washers to wear out, but requires the user to exert more torque on the flush lever in order to lift water up into the siphon passageway before the flow begins.

  Pressure-assisted toilets use compressed air trapped inside a plastic tank hidden within the ceramic cistern. When the tank fills with water, the trapped air compresses. Flushing releases the pressurized water at a flow rate much higher than a gravity-flow toilet. These toilets resist clogging but carry financial and safety drawbacks: they cost more to buy, the plastic tanks need replacing roughly every 10 years, and they are noticeably noisier. A massive recall beginning in 2012 covered more than 1.4 million toilets equipped with pressure-assisted tanks after reports of the tanks exploding and causing serious injuries.

• 7. Water Conservation

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  Since 1994, the United States has enforced a significant change in how much water a toilet is permitted to use. Pre-1994 residential toilets typically used 3.4 US gallons per flush. The Energy Policy Act of 1992, passed by Congress, mandated that common flush toilets use no more than 1.6 US gallons from 1994 onward. Early low-flow models drew complaints because they often required more than one flush to remove solid waste. Some consumers, unhappy with the performance, drove across the border to Canada or Mexico or bought salvaged toilets from older buildings.

  Manufacturers responded by refining their designs. The improved products became known as high efficiency toilets, or HETs. An HET has an effective flush volume of 1.3 US gallons or less and may be single-flush or dual-flush. The US Environmental Protection Agency uses a Maximum Performance, or MaP, score of 350 as the minimum performance threshold for HETs. A toilet that scores 1,000 on the MaP scale should remove all waste in a single flush, not clog, harbor no odor, and be easy to keep clean.

  Some newer designs combine pressure-assist technology with bowl and trapway geometry engineered to enhance the siphon effect. These use as little as 0.8 US gallons per flush, or as little as 0.5 US gallons for the reduced-volume cycle in dual-flush models. Urine diversion flush toilets, developed in Sweden, save water by using less water or even no water for the urine flush, compared to around 6 litres for a feces flush. Raw water flushing systems, using seawater rather than potable water, are in use in the majority of cities and towns in Hong Kong, in Gibraltar, and in Avalon, California.

• 8. Myths and Language

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  The idea that water swirls clockwise south of the equator and counter-clockwise north of it, because of the Coriolis effect, is a widespread misconception. The direction water takes in a flushing toilet is determined almost entirely by the angle at which the bowl's rim jets are pointed during manufacture. The Rossby number, a ratio used to assess the relative importance of the Coriolis force, reaches into the billions on the scale of a toilet bowl. At that scale, the Coriolis effect is too weak to be observed except under carefully controlled laboratory conditions.

  The word "toilet" itself has a history worth noting. It originally meant "wash-room", with no connection to sanitary facilities. Early indoor facilities were called garderobes because the rooms were used to store clothes: ammonia fumes from the contents were found to deter fleas and moths. From the 16th century onward in England, a private room containing a flushing toilet became known as a Water Closet, or WC, to distinguish it from an Earth Closet.

  The abbreviation WC traveled widely across Europe. French speakers adopted aller aux waters, meaning "to go to the waters". Romanian picked up veceu, Finnish adopted vessa, and German uses Klo, from the first syllable of Klosett. Italian speakers use both WC and the word water for the fixture itself. The American slang term "the john" is said to derive from water closets installed at Harvard University in 1735, which bore the name of their manufacturer, Rev. Edward Johns. Johns introduced his Dolphin toilet to the United States at the 1876 Centennial Exposition in Philadelphia. The courtesy flush, described since the 1990s as a mid-defecation flush performed as a consideration to others sharing a bathroom, is a more recent addition to the toilet's social vocabulary.