Chlorination of the U.S. Water Supply Begins Summary

  • Last updated on November 10, 2022

Water treatment plants in the United States began to use chlorination to kill bacteria that had been causing epidemics.

Summary of Event

Before the introduction of chlorine into drinking-water supplies, epidemics of infectious diseases caused by waterborne microorganisms were common. Such epidemics occurred regularly in the United States and the rest of the world, particularly in urban areas. Pollution;water Water;treatment Chlorination of water (U.S.) Medicine;waterborne diseases Sanitation;water supply Public health concerns;water quality [kw]Chlorination of the U.S. Water Supply Begins (1908) [kw]U.S. Water Supply Begins, Chlorination of the (1908) [kw]Water Supply Begins, Chlorination of the U.S. (1908) Pollution;water Water;treatment Chlorination of water (U.S.) Medicine;waterborne diseases Sanitation;water supply Public health concerns;water quality [g]United States;1908: Chlorination of the U.S. Water Supply Begins[02000] [c]Health and medicine;1908: Chlorination of the U.S. Water Supply Begins[02000] [c]Science and technology;1908: Chlorination of the U.S. Water Supply Begins[02000] [c]Biology;1908: Chlorination of the U.S. Water Supply Begins[02000] Snow, John Koch, Robert Pasteur, Louis Simpson, James Castner, Hamilton Young

Mortality rates in the United States rose through the eighteenth and nineteenth centuries, peaking in the 1860’s and 1870’s. This rise in mortality was primarily a result of increasing urbanization. As population density increased in the cities, two interrelated problems developed: increasing demand for (along with decreasing supply of) clean water and a lack of means for disposing of human waste. As human waste entered drinking-water supplies, several types of disease-causing bacteria spread throughout the population. This spread caused a number of epidemics, including repeated occurrences of cholera and typhus.

The United States experienced epidemics throughout the nineteenth and early twentieth centuries; yellow fever epidemics occurred in 1853, 1878, and 1905, and repeated cholera epidemics included a major outbreak in the Mississippi River Valley in 1873. Diseases;cholera Diseases;yellow fever Yellow fever Cholera The initial medical and governmental responses to such outbreaks consisted of the quarantine of carriers. In particular, ships arriving in port from epidemic areas were quarantined. This response probably reduced the transmission of disease, but it did not address the role of sanitation in preventing the spread of disease.

It had long been understood that water-supply problems contribute to disease; such concerns, however, had to do with the quantity of water rather than the quality. It was generally believed that communities could minimize diseases by watering down dusty streets and alleys. Any concerns with water quality tended to emphasize clarity and smell of drinking water, rather than its biological cleanliness.

During a 1793 yellow fever epidemic in Philadelphia, more than seventeen thousand people—more than 10 percent of the city’s population—contracted the disease. This event led to the establishment in Philadelphia in the late 1790’s of the first municipal waterworks in the United States. The creation of the waterworks not only led to a decrease in epidemic diseases in Philadelphia but also signaled a shift to the notion that water supply should be a public utility function.

The quality of water supplies was first addressed in England in 1829, when James Simpson, the engineer of the Chelsea waterworks, invented and constructed the first water-filtering system. Simpson’s sand filters were designed to remove visible dirt from the water supply, which they did, but as an invisible and unrecognized side benefit, the filters also removed some disease-causing bacteria. The concept of filtration slowly caught hold, and by 1852 all water companies supplying water for domestic use in London and drawing their water from the River Thames were required to use filters.

The first person to recognize that the incidence of disease was directly related to drinking-water supplies was the English anesthesiologist John Snow, who proved that cholera outbreaks in 1849 and 1854 were related to water sources. He showed definitively that the cholera outbreak in London in 1854 resulted from the drinking of water from the Broad Street pump, the waters of which were polluted with human excrement. He surmised that a poison was responsible for the cholera, but he could not identify the poison.

The French chemist Louis Pasteur developed the science of bacteriology in the 1860’s and expounded the germ theory of disease. He proved that diseases do not spread when the bacteria that cause them are killed. Robert Koch, a German country doctor and bacteriologist, first identified the bacterium that causes cholera in 1883.

In the 1870’s, standard testing of water began, but the tests were aimed at finding only chemical, not biological, impurities. In the mid-1880’s, biological testing began, and it became apparent that filtration removed about 98 percent of the bacteria in water. Filtration, which had been developed for the biologically contaminated waters of Europe, was a more difficult process for the silt-laden waters in the United States. By 1900, the common water treatment method in the United States was chemical coagulation, usually achieved by the application of aluminum sulphate, followed by filtration. This removed most, but not all, of the disease-causing bacteria.

The American chemist Hamilton Young Castner developed a process for manufacturing sodium hydroxide from seawater in 1894; Castner’s process created chlorine as a by-product. The chlorine thus produced was initially used primarily as a bleaching agent in the paper and fabric industries, but this ready supply of chlorine would ultimately play a crucial role in destroying bacteria in drinking water.

Chlorine and chlorine compounds had been used since the beginning of the nineteenth century as deodorants and as preservatives of organic matter. These compounds had been used on raw sewage but had not been used as disinfectants for drinking water. In 1896, chlorine was used for the first time to destroy bacteria in a drinking-water supply, successfully stopping a typhoid epidemic.

As a result of the increased knowledge about bacteria, their role in causing disease, and their vulnerability to chlorine, the modern method of water treatment evolved over the following ten years. By 1908, standard methods of water treatment had been developed and were coming into use in major U.S. metropolitan areas. The water treatment methods included the application of a chemical coagulating agent to aid filtration; the filtration itself, which removed suspended particles and most bacteria; and a final treatment with chlorine or a chlorine compound to kill remaining bacteria.


The introduction of chlorine to the water treatment process to destroy waterborne bacteria nearly eliminated disease caused by bacteria from drinking water in the United States and the rest of the developed world, with a consequent reduction in mortality rates. This was a combined effect of the technology available to destroy the bacteria and the establishment of laws and regulations to ensure the technology is used. Today, isolated instances of bacterial infection caused by polluted water still occur in the developed world, but they are rare. Epidemics attributable to waterborne bacteria no longer occur in the developed world, although they still occur in less developed countries where water supplies are polluted.

As a part of the bureaucracy that developed to regulate the quality of U.S. water supplies, the U.S. Public Health Service Public Health Service, U.S. was established in 1912. Among its activities were the development of standards for drinking water and the education of the public about the dangers of drinking polluted water.

Early successes in destroying disease-causing bacteria in the water supply fostered a false belief in the cleanliness of water in the United States. Officials believed that as long as water could be disinfected to destroy harmful bacteria, there were no problems with the water supply. This assumption led to increasing pollution of rivers, streams, and groundwater, because people believed that filtration and disinfection would make water safe. The pollution took two forms: biological pollution, caused by sewage emitted into rivers and streams, and chemical pollution, caused by industrial and agricultural emissions. Filtration and disinfection methods can, in most cases, counteract the effects of biological pollutants in water supplies, but these methods do not reduce chemical pollution—in fact, they contribute to it.

In the first half of the twentieth century, two technologies related to the chlorination of water were constantly and incrementally improved: the technology for controlling the amount of chlorine added to water and the technology for testing water for bacterial contamination. Combined, these allowed a reduction in the amount of chlorine added to water supplies, lowering costs for water-supply companies, minimizing the chlorine smell and taste of treated water, and ensuring the biological cleanliness of the water.

Depending on its source, water may contain a number of dissolved minerals as impurities. Two of these minerals, calcium and magnesium, are the main minerals that cause water hardness, which can leave mineral deposits on plumbing fixtures and increases the amount of soap needed to mix with water to achieve cleanliness. These minerals may be a nuisance, but, unlike disease-causing bacteria, they are not harmful to humans. In the 1870’s, standard tests for minerals in water were established, and by the end of the nineteenth century, chemical means had been developed to remove some dissolved minerals. These included the addition of small amounts of lime to remove calcium and the addition of sodium and potassium salts to remove other minerals. In 1906, the principle of ion exchange was developed, whereby dissolved nuisance minerals were replaced by other chemical ions that were considered less troublesome. These methods, however, were used only to remove natural impurities that did not pose a danger to humans.

Successful water treatment to counteract the effects of biological pollution and natural minerals gave officials and the public a false sense of security about the safety of water supplies. In the second half of the twentieth century, concerns were raised about chemical pollution of the water supply. A large number of different chemical pollutants can enter the water supply from two main sources: agricultural runoff and industrial waste. The health effects of such pollutants differ from those of bacteria; the health dangers of bacteria are severe and acute, whereas the dangers of chemical pollution build up over long periods. The dangers and effects of long-term chemical pollution are much more difficult to isolate than the dangers of exposure to bacteria. The human population is exposed to numerous chemical compounds over time, and it is difficult to assign a degree of danger to each individual chemical.

Chemical pollutants in water can be partially removed through chemical filtering, but the risks posed by residual amounts of chemicals are still undetermined. In the second half of the twentieth century, the bulk of the work on water treatment centered on the elimination of sources of chemical pollution rather than on the removal of chemicals from the water supply.

In the 1970’s, a new source of chemical pollution of the water supply was discovered. The chlorine that was being used to destroy bacteria combined with organic matter in the water to form trihalomethanes (THMs), which in high concentrations can cause cancer. Thus chlorine, which had been used to make water safe, was shown to introduce a new risk. This discovery raised a new set of questions. If water is not disinfected, waterborne diseases that could be deadly may result, and the effects would be rapid. If chlorine is used to disinfect water, the short-term results are favorable, but the long-term effects are unclear. Large concentrations of THMs are known to cause cancer, but the effects of small concentrations are unknown, and there is no clear threshold concentration below which humans are safe.

The THM findings left in their wake a debate as to the best method for disinfecting water. As of the early twenty-first century, major options for water treatment include chlorination, with its proven effectiveness in eliminating disease caused by bacteria but its unknown long-term effects; other chemical treatments, including the application of ozone, that have varying effects on bacteria and that may have unknown side effects; and nonchemical treatments, such as disinfection with light, heat, or nuclear particles. Pollution;water Water;treatment Chlorination of water (U.S.) Medicine;waterborne diseases Sanitation;water supply Public health concerns;water quality

Further Reading
  • citation-type="booksimple"

    xlink:type="simple">Baker, M. N. The Quest for Pure Water. New York: American Water Works Association, 1949. A historical look at water treatment, especially in the United States. Includes descriptions of various techniques and equipment.
  • citation-type="booksimple"

    xlink:type="simple">Degremont, G. Water Treatment Handbook. 6th ed. New York: Springer-Verlag, 1991. A complete technical discussion of the biological, chemical, and physical aspects of water and water treatment. Includes photographs and diagrams.
  • citation-type="booksimple"

    xlink:type="simple">Gottlieb, Robert. A Life of Its Own: The Politics and Power of Water. San Diego: Harcourt Brace Jovanovich, 1988. A good history of the politics of water supply in the western United States. Includes good descriptions of changes in attitudes and concerns.
  • citation-type="booksimple"

    xlink:type="simple">Mughat, F. H. “Chlorination of Drinking Water and Cancer: A Review.” Journal of Environmental Pathology 7 (September 1, 1992): 287-294. A review of research regarding chlorination of drinking water and the incidence of cancer in humans.
  • citation-type="booksimple"

    xlink:type="simple">Powledge, Fred. Water: The Nature, Uses, and Future of Our Most Precious and Abused Resource. New York: Farrar, Straus and Giroux, 1982. A detailed treatment of water and the supply of water from the standpoints of both quality and quantity.
  • citation-type="booksimple"

    xlink:type="simple">Smith, Norman Alfred Fisher. Man and Water: A History of Hydro-technology. New York: Charles Scribner’s Sons, 1975. A good history of water-supply technology. Bibliography.
  • citation-type="booksimple"

    xlink:type="simple">White, George Clifford. Handbook of Chlorination and Alternative Disinfectants. 4th ed. New York: John Wiley & Sons, 1998. Reference work on all aspects of water purification with chlorine and other disinfectants. Aimed at professionals in industries such as water treatment, toxicology, environmental engineering, and food packaging.

Euthenics Calls for Pollution Control

Steinmetz Warns of Pollution in “The Future of Electricity”

New York City Institutes a Comprehensive Zoning Law

Izaak Walton League Is Formed

Wolman Begins Investigating Water and Sewage Systems

Arbitration Affirms National Responsibility for Pollution

Categories: History