For years, a primary metaphor for the internet has been the “town square,” an endless space for free expression where everyone can have their say. But as scaled digital platforms have grown to dominate most of modern life, metaphors centered solely on speech have failed to explain our current civic dysfunction.

Perhaps the better way to understand the internet is to compare it to a much older infrastructure problem: citywide sanitation systems. Posted content is akin to water; websites and other interfaces are analogous to pumps; and unintended feedback loops correspond to risk of infection. A public-health framework for understanding the internet would focus not on online information itself but on how it is generated, spread, and consumed via digital platforms.

This model’s genesis lies in the two-century-old story of early advocates for clean water in Victorian England. At the time, the life-threatening diseases that ravaged cities—cholera, typhus, tuberculosis, and scarlet fever—were not new. What were new were modern living conditions. Infections that might have taken weeks to spread through a village suddenly ravaged whole populations within days, and no one understood what was causing the massive outbreaks.

The Victorian working classes knew whom to blame when disease broke out: doctors. Mobs assaulted members of the medical establishment, leaving government officials unsure how to weigh the safety of physicians against the public interest. Why the rage? The traditional response to disease—quarantines—had become ineffective in industrialized cities, prompting the public to distrust those who profited from treatment.

The first serious approach to the problem was taken by a coalition of doctors, liberal advocates, and social reformers starting in the 1830s. Known as miasmists, they pushed the idea that noxious air was the culprit in epidemics. If a neighborhood could not pass the smell test, the argument went, one immediately knew it was already too late to be saved.

Miasmists, including prominent ones such as Florence Nightingale, have an ambivalent legacy. They were among the first to emphasize that disease had not just biological but also social and economic causes, a crucial insight. But simultaneously, they were dead wrong about the role of air in the spread of the common diseases of the time, a reflection of an elitist worldview and overprescribed morality.

This tension revealed itself during two key events. One was the Great Stink of 1858, in which a combination of hot weather and poor waste disposal transformed the Thames into a cesspool. The stench was so bad that even the curtains of the houses of Parliament had to be caked with lime. No one was safe from the foul air, and by the miasmists’ assumptions, that meant that no one was safe from disease. But, in fact, no major outbreak followed the Great Stink.

Second was the groundbreaking work of a brilliant doctor, John Snow, who had suspected for years that water (not air) was the actual cause of urban epidemics. In a painstaking natural experiment, Snow demonstrated that the Broad Street pump was the source of the 1854 cholera epidemic in the Soho area of London. His data revealed that residents living across the city became sick if they happened to get water from the pump, even while a nearby brewery that drew its water from a different source had no recorded cases. There was no other reasonable explanation: Some as-yet-undiscovered mechanism, localized at the pump, was responsible for infection. Though Snow was careful to frame his results so as not to explicitly reject the miasma theory, the implications were obvious.