in their seminal 1914 paper, and the first full-scale continuous-flow system was installed at worcester two years later. in the aftermath of the first world war the new treatment method spread rapidly, especially to the us, denmark, germany and canada. by the late 1930s, the activated sludge treatment became a well-known biological wastewater treatment process in those countries where sewer systems and sewage treatment plants were common. toilets further information: toilet § history with the onset of the industrial revolution and related advances in technology, the flush toilet began to emerge into its modern form in the late 18th century, (see development of the modern flush toilet.) in urban areas, toilets are typically connected to a municipal sanitary sewer system, while in more rural areas they are usually connected to an onsite sewage facility (septic system). where this is not feasible or desired, dry toilets are an alternative option. water supply chelsea waterworks, 1752. two newcomen beam engines pumped thames water from a canal to reservoirs at green park and hyde park. an ambitious engineering project to bring fresh water from hertfordshire to london was undertaken by hugh myddleton, who oversaw the construction of the new river between 1609 and 1613. the new river company became one of the largest private water companies of the time, supplying the city of london and other central areas. the first civic system of piped water in england was established in derby in 1692, using wooden pipes, which was common for several centuries. the derby waterworks included waterwheel-powered pumps for raising water out of the river derwent and storage tanks for distribution. it was in the 18th century that a rapidly growing population fueled a boom in the establishment of private water supply networks in london. the chelsea waterworks company was established in 1723 "for the better supplying the city and liberties of westminster and parts adjacent with water". the company created extensive ponds in the area bordering chelsea and pimlico using water from the tidal thames. other waterworks were established in london, including at west ham in 1743, at lea bridge before 1767, lambeth waterworks company in 1785, west middlesex waterworks company in 1806 and grand junction waterworks company in 1811. the s-bend pipe was invented by alexander cummings in 1775 but became known as the u-bend following the introduction of the u-shaped trap by thomas crapper in 1880. the first screw-down water tap was patented in 1845 by guest and chrimes, a brass foundry in rotherham. sand filter sir francis bacon attempted to desalinate sea water by passing the flow through a sand filter. although his experiment did not succeed, it marked the beginning of a new interest in the field. the first documented use of sand filters to purify the water supply dates to 1804, when the owner of a bleachery in paisley, scotland, john gibb, installed an experimental filter, selling his unwanted surplus to the public. this method was refined in the following two decades by engineers working for private water companies, and it culminated in the first treated public water supply in the world, installed by engineer james simpson for the chelsea waterworks company in london in 1829. this installation provided filtered water for every resident of the area, and the network design was widely copied throughout the united kingdom in the ensuing decades. the metropolis water act introduced the regulation of the water supply companies in london, including minimum standards of water quality for the first time. the act "made provision for securing the supply to the metropolis of pure and wholesome water", and required that all water be "effectually filtered" from 31 december 1855. this was followed up with legislation for the mandatory inspection of water quality, including comprehensive chemical analyses, in 1858. this legislation set a worldwide precedent for similar state public health interventions across europe. the metropolitan commission of sewers was formed at the same time, water filtration was adopted throughout the country, and new water intakes on the thames were established above teddington lock. automatic pressure filters, where the water is forced under pressure through the filtration system, were innovated in 1899 in england. water chlorination in what may have been one of the first attempts to use chlorine, william soper used chlorinated lime to treat the sewage produced by typhoid patients in 1879. in a paper published in 1894, moritz traube formally proposed the addition of chloride of lime (calcium hypochlorite) to water to render it "germ-free." two other investigators confirmed traube's findings and published their papers in 1895. early attempts at implementing water chlorination at a water treatment plant were made in 1893 in hamburg, germany, and in 1897 the town of maidstone, in kent, england, was the first to have its entire water supply treated with chlorine. permanent water chlorination began in 1905, when a faulty slow sand filter and a contaminated water supply led to a serious typhoid fever epidemic in lincoln, england. dr. alexander cruickshank houston used chlorination of the water to stem the epidemic. his installation fed a concentrated solution of chloride of lime to the water being treated. the chlorination of the water supply helped stop the epidemic and as a precaution, the chlorination was continued until 1911 when a new water supply was instituted. manual control chlorinator for the liquefaction of chlorine for water purification, early 20th century. from chlorination of water by joseph race, 1918. the first continuous use of chlorine in the united states for disinfection took place in 1908 at boonton reservoir (on the rockaway river), which served as the supply for jersey city, new jersey. chlorination was achieved by controlled additions of dilute solutions of chloride of lime (calcium hypochlorite) at doses of 0.2 to 0.35 ppm. the treatment process was conceived by dr. john l. leal and the chlorination plant was designed by george warren fuller. over the next few years, chlorine disinfection using chloride of lime were rapidly installed in drinking water systems around the world. the technique of purification of drinking water by use of compressed liquefied chlorine gas was developed by a british officer in the indian medical service, vincent b. nesfield, in 1903. according to his own account, "it occurred to me that chlorine gas might be found satisfactory ... if suitable means could be found for using it.... the next important question was how to render the gas portable. this might be accomplished in two ways: by liquefying it, and storing it in lead-lined iron vessels, having a jet with a very fine capillary canal, and fitted with a tap or a screw cap. the tap is turned on, and the cylinder placed in the amount of water required. the chlorine bubbles out, and in ten to fifteen minutes the water is absolutely safe. this method would be of use on a large scale, as for service water carts." u.s. army major carl rogers darnall, professor of chemistry at the army medical school, gave the first practical demonstration of this in 1910. shortly thereafter, major william j. l. lyster of the army medical department used a solution of calcium hypochlorite in a linen bag to treat water. for many decades, lyster's method remained the standard for u.s. ground forces in the field and in camps, implemented in the form of the familiar lyster bag (also spelled lister bag). this work became the basis for present day systems of municipal water purification. fluoridation further information: history of water fluoridation water fluoridation is a practice adding fluoride to drinking water for the purpose of decreasing tooth decay. the architect of these first fluoride studies was dr. h. trendley dean, head of the dental hygiene unit at the national institute of health (nih). dean began investigating the epidemiology of fluorosis in 1931. by the late 1930s, he and his staff had made a critical discovery. namely, fluoride levels of up to 1.0 ppm in drinking water did not cause enamel fluorosis in most people and only mild enamel fluorosis in a small percentage of people. proof that fluoride prevents caries this finding sent dean's thoughts spiraling in a new direction. he recalled from reading mckay's and black's studies on fluorosis that mottled tooth enamel is unusually resistant to decay. dean wondered whether adding fluoride to drinking water at physically and cosmetically safe levels would help fight tooth decay. this hypothesis, dean told his colleagues, would need to be tested. in 1944, dean got his wish. that year, the city commission of grand rapids, michigan-after numerous discussions with researchers from the phs, the michigan department of health, and other public health organizations-voted to add fluoride to its public water supply the following year. in 1945, grand rapids became the first city in the world to fluoridate its drinking water. the grand rapids water fluoridation study was originally sponsored by the u.s. surgeon general, but was taken over by the nidr shortly after the institute's inception in 1948. trends the sustainable development goal 6 formulated in 2015 includes targets on access to water supply and sanitation at a global level. in developing countries, self-supply of water and sanitation is used as an approach of incremental improvements to water and sanitation services, which are mainly financed by the user. decentralized wastewater systems are also growing in importance to achieve sustainable sanitation. understanding of health aspects original map by john snow showing the clusters of cholera cases in the london epidemic of 1854. the greek historian thucydides (c. 460 – c. 400 bc) was the first person to write, in his account of the plague of athens, that diseases could spread from an infected person to others. the mosaic law, within the first five books of the hebrew bible, contains the earliest recorded thoughts of contagion in the spread of disease. specifically, it presents instructions on quarantine and washing in relation to leprosy and venereal disease one theory of the spread of contagious diseases that were not spread by direct contact was that they were spread by spore-like "seeds" (latin: semina) that were present in and dispersible through the air. in his poem, de rerum natura (on the nature of things, c. 56 bc), the roman poet lucretius (c. 99 bc – c. 55 bc) stated that the world contained various "seeds", some of which could sicken a person if they were inhaled or ingested. the roman statesman marcus terentius varro (116–27 bc) wrote, in his rerum rusticarum libri iii (three books on agriculture, 36 bc): "precautions must also be taken in the neighborhood of swamps ... because there are bred certain minute creatures which cannot be seen by the eyes, which float in the air and enter the body through the mouth and nose and there cause serious diseases." the greek physician galen (ad 129 – c. 200/216) speculated in his on initial causes (c. 175 ad that some patients might have "seeds of fever". in his on the different types of fever (c. 175 ad), galen speculated that plagues were spread by "certain seeds of plague", which were present in the air. and in his epidemics (c. 176–178 ad), galen explained that patients might relapse during recovery from fever because some "seed of the disease" lurked in their bodies, which would cause a recurrence of the disease if the patients did not follow a physician's therapeutic regimen. the fiqh scholar ibn al-haj al-abdari (c. 1250–1336), while discussing islamic diet and hygiene, gave advice and warnings about impurities that contaminate water, food, and garments, and could spread through the water supply. long before studies had established the germ theory of disease, or any advanced understanding of the nature of water as a vehicle for transmitting disease, traditional beliefs had cautioned against the consumption of water, rather favoring processed beverages such as beer, wine and tea. for example, in the camel caravans that crossed central asia along the silk road, the explorer owen lattimore noted, "the reason we drank so much tea was because of the bad water. water alone, unboiled, is never drunk. there is a superstition that it causes blisters on the feet." one of the earliest understandings of waterborne diseases in europe arose during the 19th century, when the industrial revolution took over europe. waterborne diseases, such as cholera, were once wrongly explained by the miasma theory, the