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How did sand filtration and chlorination reduce cholera and typhoid fever?

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Diagram of a water treatment plant showing the process from water inlet through mixing, coagulation, flocculation, settling, filtering, chemical treatment with chlorine, storage, and high-lift pumping to the distribution system. — water purification Water from inlets located in the water supply, such as a lake, is sent to be mixed, coagulated, and flocculated and is then sent to the waterworks for purification by filtering and chemical treatment. After being treated, the water is pumped into water mains for storage or distribution.

Sand filtration and chlorination were pivotal in the late 19th and early 20th centuries for eliminating waterborne diseases like cholera and typhoid fever by removing or destroying pathogenic microorganisms.1

Sand Filtration

Filtration is a physical process that removes suspended impurities by percolating water through a bed of porous material, such as sand. This process traps suspended particles, harmful protozoa, and natural color within the filter media. By clarifying the water, filtration also prevents suspended matter from shielding microbes during the subsequent disinfection stage.2

Chlorination

Chlorination involves adding chlorine or chlorine compounds to water to destroy pathogenic bacteria. Typically the final step in treatment, it ensures a residual concentration of disinfectant remains throughout the distribution system, providing ongoing protection against contamination.43

Together, these technologies established a scientific basis for public health, as their implementation led to the virtual elimination of these deadly diseases in developed countries.1