“I can only say that when you have once put sewage into the water, I should be rather reluctant to drink it.” If only Londoners had been in a position to follow the example of Sir Benjamin Brodie, Oxford professor of chemistry, in the evidence he gave to a Victorian committee of enquiry into the capital’s water quality. But for much of the period covered by Nick Higham’s intriguing new book, they weren’t. In fact, their water, when they got any, was a rather disgusting cocktail of organic and inorganic ingredients. The wonder is that so many citizens survived the experience. Londoners must have had strong stomachs.

And reader, beware. You’ll need a strong stomach yourself to absorb some of Higham’s descriptions of the Thames and its tributaries. Dead cats, drowned puppies, stinking butchers’ offal and islands of excrement float serenely through the pages like stately barges, undisturbed by the affairs of men.

On its murky surface, The Mercenary River is a gruesome yet fascinating tale of how London came to be supplied with water. Beginning in the Middle Ages, when people without a well of their own simply dipped a bucket in the Thames, Higham goes on to explore the impact of the New River Company, which at the beginning of the 17th century created a 38-mile-long channel snaking south from Hertfordshire and which still, more than 400 years after it was completed, supplies around 10 per cent of London’s drinking water. Other private water companies joined in, most drawing their supply from the Thames, unmindful of the fact that it was an open sewer.

Soon there was an entire industry devoted to London’s water supply: collectors, who brought in the money from householders; surveyors, who kept an eye on the state of the river; paviours, who connected up the thin elm pipes and repaired the roads afterwards; and turncocks, who turned the supply on and off at predetermined times. John Aubrey noted in 1682 that “London is grown so populous and big that the New River… can serve the pipes to private houses but twice a week.” And although the frequency of supply, if not the quality, gradually improved, Londoners still had no constant supply of water until the late 19th century, with the water companies stubbornly maintaining that if it was “on” tap day and night, the poor would simply let it dribble away, along with the companies’ profits.

But The Mercenary River is rather more than a simple account of the march of progress. Right up to 1902, when the Metropolis Water Act established the Metropolitan Water Board, London’s water supply was in the hands of half a dozen or so private companies, all of them determined to put the interests of their shareholders some way before the welfare of their customers. And this is where the story really gets interesting. All the expected Victorian heroes put in appearances: John Snow, who established that cholera was carried in polluted water; the social reformer Edwin Chadwick, taking time off from reforming the Poor Laws to publish his groundbreaking Report on the Sanitary Condition of the Labouring Population of Great Britain; and Joseph Bazalgette, whose system of intersecting sewers did so much to clean up the Thames.