A short history of water supply

Humans engineered water supply for four thousand years before understanding what made water dangerous. The gap between those two achievements is the most striking thing about this history.

Engineering first

The Indus Valley cities of Mohenjo-daro and Harappa had planned wells, drainage and bathing structures by around 2600 BC. Persian qanats — gently sloping tunnels tapping groundwater and conveying it for tens of kilometres entirely by gravity — spread across arid Asia from around 600 BC, and some remain in use.

Rome eventually operated eleven aqueducts delivering water by gravity from up to ninety kilometres away, with distribution to public fountains, baths and some private supply. The engineering was superb. The understanding of why water mattered to health was essentially absent: Rome’s lead pipes are famous, and Roman authors noted that lead workers became ill without connecting it to the water supply.

The nineteenth century turn

Paisley installed the first treated municipal supply using slow sand filtration in 1804 — decades before anyone knew why filtration helped. It was done for clarity and taste. The health benefit was accidental and enormous.

In 1854, John Snow mapped cholera deaths in Soho against water sources and demonstrated that the disease was waterborne, against the prevailing miasma theory that attributed it to bad air. Four years later the Great Stink drove Parliament to fund Bazalgette’s intercepting sewers, sized at roughly double the calculated requirement — a decision that served London for a century and a half.

Chlorination

Continuous chlorination of public supply began in Belgium in 1902 and in the United States in 1908. Typhoid death rates in chlorinated cities collapsed within a few years. It is, by a wide margin, the most consequential public health intervention in the history of water, and probably one of the most consequential of any kind.

It is worth holding that alongside modern concern about disinfection by-products. The by-products are real and regulated. The alternative — not disinfecting — killed people in numbers that are difficult to convey.

The modern era

The twentieth century added the activated sludge process for wastewater in 1914, practical reverse osmosis membranes in 1959, and — from the 1970s — comprehensive regulation of drinking water quality and of discharges. The twenty-first century has been dominated by contaminants that earlier treatment was never designed for: PFAS, pharmaceuticals and microplastics.