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Croton Aqueduct
The honest starting point. New York lost 3,500 people to cholera in 1832, when its water came from wells, ponds and springs inside the city. The aqueduct's answer was a 41-mile channel carrying Croton River water, largely by gravity, which arrived on July 4, 1842.
Clean water reached the city, but not every home. Cholera came back with greater force in the Sixth Ward in 1849, and a study of ward records found cholera deaths tracked where Croton pipes did and did not reach. That is the lesson every later entry absorbs: a pure source protects only the people it is piped to.
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London sewer system
The clearest natural experiment on the list came from the one district the system had not yet reached. Joseph Bazalgette's sewers were begun in 1859, after the Great Stink of 1858 finally forced Parliament to act over the state of the Thames, and completed in 1875.
In June 1866 cholera broke out in east London, where homes were not yet connected. William Farr found 93% of deaths fell within the East London Waterworks Company's area, where about 4,000 people died, while the rest of the city was spared. Bazalgette installed temporary pumps at Abbey Mills and within weeks diverted local sewage into the new Northern Outfall sewer. It was London's last cholera epidemic.
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Paris sewers
Paris is the case for building supply and drainage together. Eugène Belgrand, a hydrologist, took over the city's water service in 1854 under Haussmann and worked both ends at once: spring water captured at its source began flowing through the network in 1865, and by 1867 the sewer galleries had been heightened so workers could move through them.
The record is less tidy than London's, which is worth knowing. Cholera still struck Paris in 1849 and again in 1884, and the network was only complete enough to carry solid waste as well as liquid sewage by 1894. Read it as a long, piecemeal job rather than a single triumph.
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Chicago Sanitary and Ship Canal
Chicago fixed its drainage twice, and the first fix created the second problem. Ellis Chesbrough, brought from Boston in 1855 to build the city's sewers, found the streets too low to drain, so Chicago raised its streets over the new sewers and jacked its buildings up to match, the six-story Tremont House included. Those sewers emptied into the Chicago River, which flowed into Lake Michigan, where the city drew its drinking water.
Typhoid deaths averaged about 65 per 100,000 a year in the late 1800s and hit 174 in 1891. The Sanitary and Ship Canal, opened in January 1900, reversed the river and sent sewage away from the lake. Treating the water from 1912 cut typhoid sharply again, so credit the decline to both, not the canal alone.
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Lawrence Experiment Station
The Lawrence city filter, 1893
This is where American water treatment proved itself with numbers. Typhoid in Lawrence and neighboring Lowell, Massachusetts, killed more than 200 people in 1890 and 1891. The state's experiment station, directed by engineer Hiram Mills, had been studying water and sewage treatment there since 1887, and the city's slow sand filter went into service in September 1893.
Once it was running, the town's typhoid death rate fell almost 78%. Few works on this list have a cleaner before and after.
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Kaltehofe Waterworks, Hamburg
Hamburg learned the lesson at the worst possible price. In 1892 it and neighboring Altona both drew water from the Elbe, but only Altona passed its supply through sand. More than 8,000 Hamburg residents died of cholera in about three months, most of them within a few weeks, and Robert Koch observed that the epidemic went right up to the Altona boundary and stopped, the two districts differing in one thing only: their water.
The city's response was this filtration plant on the island of Kaltehofe, designed by Franz Andreas Meyer, planner of the Speicherstadt, and running from May 1893. Its old filter basins survive in a park on the island, a rare chance to see a nineteenth-century water defense laid out in the open.
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Old River Station, Cincinnati Water Works
Cincinnati shows what filtration did for a city drinking from a busy river. The Old River Station, built from 1898 to 1907 on the Ohio about 10 miles upstream, used the rapid sand filtration process George W. Fuller had researched, with the Eden Park water works serving as the testing site, and the new system went into operation in November 1907.
The yearly typhoid toll tells the story: 239 deaths in 1906, 157 in 1907, 67 in 1908, the first year of filtration, and 46 in 1909. For a reader who wants the drop in plain numbers, this is the entry.
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Boonton Reservoir
Continuous chlorination, September 26, 1908
The quietest revolution on the list. Jersey City's new reservoir at Boonton was in court over whether its water was always pure, in a city where typhoid deaths had regularly topped 60 per 100,000 a year between 1880 and 1895. John Leal, a physician advising the water company, and engineer George W. Fuller spent 99 days secretly building a chlorine feed, without telling the city, and opened the valves on September 26, 1908.
Chlorine had been used before mainly as an emergency measure; this was the first time a US city supply was treated continuously. The effect on typhoid was detectable within months, and within a few years most American municipal supplies were using chlorine.
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Clean Air Act 1956
The one entry about air rather than water, and it earns its place on the death toll that prompted it. London's Great Smog of December 1952 killed an estimated 4,000 people across five days, with later estimates of 12,000 once the longer-term effects were counted.
The Clean Air Act 1956 created smoke-free areas across London and regulated coal burning in homes and factories. Coal slowly gave way to gas, and power stations were moved out of the capital. The same logic as the sewers applies: deal with the source, not the sick.
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