Modern New Yorkers take clean drinking water, flowing at the turn of a spigot, for granted. The working-class Victorian Londoners of Steven Johnson’s “The Ghost Map” (Riverhead Books, 301 pages, $26.95) would have found this miraculous: They drank water drawn by hand with pumps from wells in the street. In late August, 1854, a well on Broad Street, renowned for its pure, good-tasting water, suddenly teemed with cholera bacteria. A leaky cesspool within three feet of the well had saturated the surrounding soil with excrement. The resulting epidemic killed nearly 700 people during the next two weeks.

No one knew any of this at the time. Most people believed cholera was miasmatic — transmitted through the air — and brusquely dismissed any suggestion of water transmission. They believed that London’s stenches were symptomatic of miasma. “All smell is disease,” as Edwin Chadwick, president of the General Board of Health, testified before a parliamentary committee.

Two men identified the source of the 1854 epidemic — Dr. John Snow, a pioneer anesthetist and epidemiologist, and the Reverend Henry Whitehead, a genial local clergyman. Snow knew the science; Whitehead knew the people. Their brave work — the two men went door to door, treating, comforting, and questioning cholera victims at the height of the epidemic — was fast, careful, and thorough. The ghost map of the title refers to a map created by Snow that showed how geographically narrow the outbreak was, reinforcing his theory that the deaths all stemmed from the water drawn from the Broad Street well. It identified the buildings in which cholera deaths had occurred and showed by the number of strokes or marks at each building how many deaths had occurred there. The strokes are “ghosts,” if you will, of the dead.

The writings of Snow and Whitehead, supplemented by Snow’s ghost map, eventually persuaded public health officials and the scientific establishment that bad water, not bad smells, transmitted the disease. As if this weren’t enough, Snow spent more than 200 pounds publishing his book on cholera. His return on the investment was fewer than four pounds.

Steven Johnson’s “The Ghost Map” revolves around a central urban problem — eliminating the human waste generated in great cities. The London of 1854 had seen its population nearly triple during the previous 50 years. Yet Victorian London had an Elizabethan infrastructure, and the increasing flow of sewage was overwhelming the cesspools and cesspits in which excrement had been dumped for generations.

The book, assembled from numerous secondary sources, is at its best in re-reporting the facts first set down by Victorian writers: an ash heap that is simply a mound of excrement the size of a “tolerably large house,”for example. In fact, the idea for this book is so good that Mr. Johnson’s inept, tone-deaf prose and insensitivity to the historical context is all the more disappointing.

To be sure, this story has a dramatic flaw: We cannot document the meeting of the heroes. All we know is that they met, they respected each other’s work, and Whitehead later expressed his admiration for Snow. But their conversations, their collaboration, and the details of their friendship are lost to us. And, alas, Mr. Johnson lacks the narrative skill to overcome this.

Moreover, Mr. Johnson’s prose is often irritating. He’s pretentious, yanking in a quote from “Middlemarch” to describe the effect of removing the Broad Street pump’s handle, for example, or referring to the “Taylorite efficiencies” of concentration camps. He can’t resist phrases like “a twenty-three year old Prussian named Friedrich Engels” or “a thirty-something radical by the name of Karl Marx.”And he’s condescending, as in this painful sentence: “A new kind of Soho native began to appear, best embodied by the son of a hosier who was born at 28 Broad in 1757, a talented and troubled child by the name of William Blake, who would go on to be one of England’s greatest poets and artists.”Apparently, Mr. Johnson believes we need to be told who Blake was.

Mr. Johnson’s greater flaw, however, is inability to see beyond the blinders of his time and social class. This can be unwittingly comic: When Johnson writes, “You could leave town for a weekend and come back to find ten percent of your neighbors being wheeled down the street in death carts,” one can’t help reflecting that 19th-century working class Londoners were unlikely to have been able ever to leave town for a weekend, if at all.

Far more inspiring and sensible, by the way, is www.johnsnowsociety.org, the site of the John Snow Society. Dedicated to preserving knowledge of Snow’s fascinating life and works, the Society also delightfully encourages its members, whenever they visit London, to gather at the John Snow pub, located at the site of the Broad Street pump and named for a man who was, alas, a teetotaler.

Mr. Bryk last wrote in these pages about George Washington Appo.