Linn Enslow
(1891 - 1957)
Born in the United States
Year of Discovery: 1919
Purifying Our Drinking Water

Scientific discoveries are often the result of collaboration. This process allows the strongest capabilities of two or more scientists to pursue a solution to a complex issue. So it was with the discovery of the precise formula for purifying water with chlorine. Linn Enslow, a chemist, met fellow scientist Able Wolman while studying at Johns Hopkins. Together, while working at the Maryland Department of Public Health, they devised a method of standardizing the use of chlorine to purify water. Though chlorination was already in use on a limited basis, it was Wolman's process that allowed purifying water through chlorination to become widespread, and it was hailed as possibly the most significant public health advance of the early twentieth century.

The early twentieth century saw the American landscape changing quickly. Cities grew at a rapid pace and modern conveniences, such as running water, became more common. But, in this case, the technological advances outpaced safety. This meant the convenience of tap water came at a potentially deadly price. City water supplies, still in their infancy, were often the unintended carriers of diseases such as typhoid, cholera, and dysentery. Prior to treating water supplies with chlorination, cities had no effective means to purify their drinking water. The water supplies were especially vulnerable during times of heavy rain, as the runoff would carry animal waste and other contaminants into the system. Chlorination was the key to preventing this. Chlorine is a greenish yellow gas, discovered in 1774, which is over two and one-half times denser than air. It is detectable, through its noxious odor, at levels as small as one part per million. It is now widely used in disinfecting processes. Chlorination allowed cities to kill deadly microorganisms and deliver fresh, pure water to their citizens. The widespread use of chlorination to purify water stopped waterborne diseases in their tracks, significantly extending average life expectations. Life Magazine, in 1997, called the purification of drinking water "probably the most significant public health advance of the millennium."

Chlorination was not a new concept. In fact, John Snow had used chlorine in the London cholera epidemic of 1854, and the first American patent for a chlorination system was granted in 1888. But, there was a problem. Though it was widely accepted that chlorine could kill bacteria, the process was still poorly understood. Chlorine was not only a powerful purifier, but it was also a powerful poison - capable of killing human beings if not used in exactly the right amounts. This left city officials in a terrible dilemma. Though they desperately wanted to purify their public water supplies, many felt the risk was simply too great. Enslow and Wolman provided the solution they needed. The pair devised a precise formula to use in chlorinating city water supplies - a formula that could be accurately applied to any water source. Enslow and Wolman analyzed all the relevant factors, including acidity, bacteria, purity, as well as factors related to taste. Their method provided the first rigorous scientific standards by which chlorination could be uniformly and safely controlled. It was the breakthrough that laid the foundation for purified water to become available throughout the world. But, their 1919 discovery was just the first step in the process. Though the process was a major public health advance, its acceptance was slow. City officials were still wary of adding a known poison to their municipal water supplies. But, in the end, the chlorination process was adopted on a widespread scale and- by 1941, 85 percent of all American water systems used chlorination to purify their supplies.  

Written by science writer, Tim Anderson

Lives Saved: Over 177,000,000

The demise of typhoid fever in the U.S. reveals Wolman and Enslow's impact: The number of typhoid cases fell from 16/100,000 in 1913 to just 2/100,000 in 1936.

Is Chlorination Still  Important Today?
In May 2000, in Walkerton, Ontario, seven people died and more than 2,300 got sick after the town's water supply became infected with E. coli and other bacteria.  The Ontario Ministry of the Attorney General found that the required chlorine levels had not been maintained, and had they been, the disaster would have been prevented. 

Key Contributors
Abel Wolman
Linn Enslow

Links to More About the Scientist & the Science
American Journal of Public Health article discussing Enslow & Wolman's work
Johns Hopkins Magazine article discussing Enslow & Wolman's work