Photographer and social reform journalist Jacob Riis helped expose the horrific conditions within the New York City tenement slums at the end of the 19th century, and he pioneered the use of flash photography to capture nighttime and indoor images of extreme poverty that many people had never seen before. Riis' 1890 book, "How the Other Half Lives," was a compelling indictment of the conditions in which immigrants were living in the New York slums.
"How the Other Half Lives was a groundbreaking book. A forceful combination of detailed analysis and revealing photojournalism put forth a highly persuasive argument for improvements in the living conditions of the city's impoverished immigrant population.
Another of Riis' accomplishments was his work in exposing a health hazard in the New York City water supply. In his 1891 story, "Some Things We Drink," which was published in the August 21, 1891 edition of the "New York Evening Sun," Riis' investigation and photographic evidence demonstrated that the watershed which supplied the city's drinking water was being sewered into by populous towns. Riis consulted with doctors to determine how long a cholera bacillus could survive and multiply in running water. He was told that it would take 7 days, which was the final point needed to present his case to his readers. As a result of the story's publication, New York purchased land around the New Croton Reservoir, about 22 miles north of the city. Riis' efforts may have prevented New Yorkers from suffering a cholera epidemic.
Because of his highly effective use and acquisition of casual (or documentary-style) photographic images, Riis is considered to be one of the fathers of photography. He was also one of the first proponents using a flash to acquire images that were previously unobtainable.