The Sewer as Public Health

The single biggest improvement in human life expectancy did not come from medicine. It came from civil engineering: separating drinking water from sewage, at municipal scale, in city after city through the second half of the nineteenth century. It cut mortality further and faster than any drug, it worked on entire populations regardless of whether anybody sought treatment, and most of it was designed and built before germ theory was generally accepted.

That last fact is the interesting one. The dominant explanation of disease at the time was miasma: bad air, rising from filth. It is wrong about the mechanism and it recommends almost exactly the right actions: clear the streets, drain the cesspits, remove the sewage, build the sewers. A wrong theory that produces the right policy is enormously difficult to dislodge, because every intervention it suggests appears to confirm it.

John Snow's cholera map of 1854 is famous and is usually described as the moment the argument was settled, which is not what happened. By mapping deaths around a single water pump in Soho he demonstrated a waterborne route. He did not have the organism (Koch identified it thirty years later) so he was arguing from distribution against a theory everybody held, and acceptance took about two decades. Anybody who believes that good evidence speaks for itself should sit with that timeline.

What actually unlocked the money in London is worse and more instructive. Three cholera epidemics killed tens of thousands without producing funding for a sewer system. Then the summer of 1858 was hot, the Thames was effectively an open sewer, and the smell became unbearable inside the Palace of Westminster. The money was voted in eighteen days. It had been refused for decades.

Joseph Bazalgette's system, begun the following year, is the archetype. Eighty-odd miles of main intercepting sewers, over a thousand miles of street sewers, designed to carry waste downstream of the city. He famously calculated the required diameter, then doubled it, on the grounds that this sort of thing is done once. London is still using it.

The pattern repeated across the industrial world, and the sequence was consistent: crisis, resistance, a triggering event that inconvenienced somebody important, and then a very large capital project that paid for itself in lives many times over. Public health history is full of this, and it is a useful corrective to any account in which evidence drives policy by itself.

The comparison still holds today, uncomfortably. Water and sanitation account for more of the global gap in child mortality than access to hospitals does. A hospital is visible, can be opened with a ceremony, and has a name on the front. A sewer is invisible, is opened by nobody, and does more. Anybody allocating a development budget is making the nineteenth century's choice again, with the nineteenth century's answer already available and generally ignored for the same reasons.