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

At the turn of the 20th century, the implementation of sand filtration and chlorination was instrumental in the virtual elimination of waterborne diseases like cholera and typhoid fever in developed countries. These technologies were adopted following the scientific validation of the germ theory of disease, which established that pathogenic microorganisms in drinking water were the primary cause of these outbreaks.1

Filtration functions as a physical process that removes suspended impurities, including harmful protozoa, by percolating water through granular media such as sand. By removing these suspended particles, filtration also prevents microbes from being shielded from subsequent disinfection processes.2

Chlorination serves as a critical disinfection step, where chlorine or its compounds are added to water to neutralize remaining pathogenic microorganisms. A key advantage of chlorination is that a residual concentration can be maintained throughout the distribution system, ensuring the water remains safe until it reaches the consumer. Together, these methods provide a multi-barrier approach to ensuring public health and water safety.13