Turn on a tap in most cities today and you can drink without a second thought. A little over a century ago, that glass of water could carry typhoid, and engineers argued over how to make it safe.
When water could kill
At the start of the 20th century, American cities were dangerous places to live. Diseases spread by dirty water, such as typhoid fever, cholera and dysentery, swept through crowded neighbourhoods, and mortality in cities was higher than in the countryside. The tools to fight back were just arriving. In 1908 Jersey City, New Jersey, became the first American city to disinfect its water supply continuously with chlorine, and the practice spread quickly.
But there was a problem. Nobody agreed on how much chlorine to use. Too little, and germs survived. Too much, and the water tasted of chemicals. Conditions differed from one supply to the next, and each water system was left to guess. Someone needed to turn the guesswork into a science.
A son of East Baltimore
Abel Wolman was born in Baltimore in 1892, the fourth of six children of Jewish immigrants from Poland. He wanted to be a doctor and earned a pre-medical degree at Johns Hopkins University in 1913, but at his mother's urging he turned to engineering instead. In 1915 he became only the fourth person to receive a degree from the university's new engineering school.
While still a student he worked on a pollution study of the Potomac River for the U.S. Public Health Service. After graduating he joined the Maryland State Department of Health, where he would later serve as chief engineer from 1922 to 1939. He lived his whole life in Baltimore, and he never stopped thinking about how engineering could protect people's health.
The formula
In 1918 Wolman teamed up with a former Hopkins classmate, the chemist Linn Enslow. Together they studied how chlorine is absorbed and used up in water, and how that depends on the bacteria in it, its acidity and other factors. From this they built a standard method for calculating the right dose for any supply, enough to kill disease-causing germs while keeping the water pleasant to drink. They published their work in March 1919 in the Journal of Industrial and Engineering Chemistry.
Wolman then did the harder work of persuading governments to use it. He applied the method to Maryland's drinking water, and by 1930 typhoid cases in the state had dropped by 92 per cent, according to the American Society of Civil Engineers. The formula came into wide use across the United States and around the world in the 1930s. The National Academy of Engineering later wrote that chlorination is frequently cited as the single most significant measure to protect public health in urban areas.
“Abel Wolman ... envisioned a world in which the most basic of necessities, water to drink, would be safe and plentiful to all peoples of the world.”Tribute in the Baltimore Evening Sun, Quoted in Memorial Tributes, Volume 5, National Academy of Engineering
Clean water and longer lives
Economists have since measured just how much difference clean water made. In a study of major American cities in the early 20th century, David Cutler and Grant Miller found that filtration and chlorination were responsible for nearly half of the total fall in deaths, three quarters of the fall in infant deaths and nearly two thirds of the fall in child deaths. They estimated that every dollar spent on these technologies returned more than 23 dollars in benefits to society.
Wolman's influence reached far beyond Maryland. He became a professor at Johns Hopkins in 1937 and helped create its department of sanitary engineering, teaching generations of engineers and public health experts. He advised cities across the United States, from New York and Detroit to Seattle, and metropolitan areas abroad including Buenos Aires, Calcutta and São Paulo. He was a consultant to more than 50 foreign governments, among them Israel, Argentina, Sri Lanka and Taiwan.
He also helped build his profession. He edited the Journal of the American Water Works Association from 1921 to 1937 and was elected president of both the American Water Works Association and the American Public Health Association. When New York City ran short of water in 1951 and again in 1965, he helped ease the crises with purified water from the Hudson River. Even at about 90 he kept an open mind: when new evidence suggested that trace chemicals in water might cause genetic damage, he changed his view and urged the people who manage water supplies to take them seriously.
Water for the world
In 1946 Wolman was a delegate to the conference that founded the World Health Organization, where he argued for environmental health to be part of its mission. Decades later, in his nineties, he was still advising the WHO on its International Drinking Water Supply and Sanitation Decade. He received the National Medal of Science in 1974 and kept working until his death in 1989 at the age of 96. A plaque at the Public Works Museum in Baltimore calls him simply "Friend of the Thirsty".
His dream is not yet complete. In August 2025 the WHO and UNICEF reported that 2.1 billion people, one in four of the world's population, still lacked safely managed drinking water. But the same report shows real progress: in rural areas, coverage of safely managed drinking water rose from 50 to 60 per cent between 2015 and 2024.
An everyday miracle
Most people never think about the chlorine in their tap water, and that is the point. Its success is measured in illnesses that never happen and children who grow up healthy. Every treatment plant that doses its water carefully carries on the work Wolman and Enslow began in Maryland more than a hundred years ago.
The goal now is to bring that same safety to every home on earth. With each new water system built in a village or a growing city, the world comes a step closer.
People in this story
Sources & further reading
- Abel Wolman, American Society of Civil Engineers
- Abel Wolman, 1892–1989 (Memorial Tributes, Volume 5), National Academy of Engineering
- Enslow, Linn Harrison, Library of Virginia, Dictionary of Virginia Biography
- The Role of Public Health Improvements in Health Advances: The 20th Century United States, National Bureau of Economic Research
- 1 in 4 people globally still lack access to safe drinking water, World Health Organization
- Abel Wolman, Wikipedia
- Water chlorination, Wikipedia
Researched from the sources above and checked against them. Spotted an error? Tell us.
Tikkun olam in action. This is part of tikkun olam, the Jewish idea of repairing the world, and every one of us can add to it.
