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(May 2005) The introduction of water filtration and chlorination in major U.S. cities between 1900 and 1940 accounted for about one-half of the 30 percent decline in urban death rates during those years, according to research published in the February 2005 issue of the journal Demography. And the study’s authors argue that their findings have relevance today in the developing world, where access to safe drinking water is growing but often still inadequate.

“Inexpensive water disinfection technologies can have enormous health returns in poor countries, even in the absence of sanitation services,” says David Cutler, a Harvard economist and co-author of the study.

Cutler and co-author Grant Miller, a Harvard graduate student, found that clean water was responsible for cutting three-quarters of infant mortality and nearly two-thirds of child mortality in the United States in the first 40 years of the 20th century—the most rapid health improvements in the nation’s history.

“Nearly all the mortality decline is accounted for by reductions in infectious disease, which today is only a small share of total mortality,” write the authors.

And although low-cost water disinfection is not a substitute for appropriate investment in sanitation, Cutler and Miller add that similar efforts to those undertaken in the United States almost 100 years ago could provide clean drinking water to many of the 1.1 billion people without access to it, thus preventing a significant share of the more than 1.7 million annual deaths from diarrhea-related diseases worldwide.

Teasing Out Why Water Treatment Made a Difference

Before water filtration, urban U.S. residents died at rates 30 percent higher than rural residents—often known as the “urban penalty.” Children faced the worst odds: In the late 1800s, infant mortality was 140 percent higher in cities than in the countryside, and child mortality was 94 percent higher. Infectious diseases accounted for 44 percent of deaths in the 13 major U.S. cities Cutler and Miller studied.

Researchers have traditionally focused on three explanations for the elimination of the urban penalty: economic innovation and nutritional gains, behavioral changes to improve hygiene, and large-scale public health innovations. But Cutler and Miller say that relatively little empirical work has examined the last factor.

The researchers focused on the role of clean water after discovering that, when a city began filtering their drinking water, deaths in that city from waterborne diseases such as typhoid fever and other infectious diseases such as pneumonia and tuberculosis declined sharply, while deaths from noninfectious diseases such as diabetes and cancer remained stable.

For their analysis, Cutler and Miller drew on U.S. Census Bureau mortality statistics while also gathering information on exactly where and when clean water technologies were introduced. Water filtration and chlorination were introduced in U.S. cities before sewage treatment, allowing the researchers to calculate the impact of each factor separately.

Cutler and Miller examined death rates before and after the introduction of clean water and compared those rates to cities that had yet to initiate water treatment. Through this “difference in difference” method, they were also able to take into account less variable trends and to rule out competing explanations for the sharp drop in mortality.

Overall, the researchers calculate that clean water was responsible for about 43 percent of the total mortality decline in the 13 cities from 1900 to 1936 (see table). Infant mortality in cities dropped 62 percent as a result of clean water. On average, water filtration reduced typhoid fever deaths by 46 percent—nearly eradicating that disease in the United States by 1936.

Table 1
Percentage of Deaths, by Cause, in Major Cities

Note: All percentages are shares of total mortality.
Source: U.S. Census Bureau’s Mortality Statistics, 1900 and 1936.

According to Cutler and Miller, the urban penalty was actually attributable to the introduction of urban sewer systems in the mid- to late-19th century. Because urban sewer systems often emptied near drinking water intake sources, cities with most highly developed sewer systems were most likely to pollute their own drinking water. Researchers think this pollution spread waterborne diseases that led to an upsurge in other contagious diseases in urban populations.

“The leading explanation seems to be that contaminated water weakens the immune system, making one susceptible to other contagious diseases, not just typhoid,” says Cutler.

Could Low-Cost Household Treatments Fill the Developing-Country Gap?

Cutler and Miller estimate that funds invested in U.S. urban water systems between 1900 and 1940 produced a social rate of return of roughly $23 for every $1 spent. And the authors write that, if increasing worldwide access to clean water today could “prevent only one percent of the 1.7 million deaths each year from diarrhea, the social rate of return would be about $160 billion.” (Their analysis assumes 30 person-years lost per death and a value for each person-year at $100,000, a standard economic practice based on research in industrialized countries that quantifies how much people must be compensated to take on risky, life-threatening jobs.)

“Water in Third World cities is not very clean; there is no reason we shouldn’t be cleaning up that water with low-cost chlorination,” Cutler argues. “It would have a large impact on health.” In 2000, the World Health Organization (WHO) and UNICEF found that more than one-fifth of the drinking water samples from existing urban water systems in developing countries were contaminated with bacteria and pollutants.

Other analysts agree with Cutler and Miller’s basic arguments. “There’s a real interaction between clean water and disease, including malaria,” says Paul McNamara, a health economist at the University of Illinois at Urban-Champaign with experience in U.S. municipal water systems and developing country finance.

But McNamara adds that, because many poor countries now spend less than $5 per capita on public health, “the question becomes which investments address public health threats and save lives at the lowest cost.” According to McNamara, widely used interventions that cost between $5 and $15 per person-year saved include anti-malarial drugs, oral rehydration kits for children with diarrheal diseases, pesticide impregnated bed nets to prevent malaria, and HIV-AIDS education.

McNamara also says that ensuring a continuous supply of clean water involves more than chlorination. “Often entire water systems are old and in disrepair,” he says. “Maintaining pipes and equipment raises public management issues, the same issues that make delivering electricity or public health programs a challenge.”

Still, there is room for optimism. Nongovernmental organizations are exploring environmentally sustainable alternatives—such as rain water “harvesting” and solar desalinization—to laying new pipe.

And simple, home-based water treatment and safe storage have proven faster and cheaper ways to provide people with safe water than waiting for new or improved piped water, says Mark Sobsey of the University of North Carolina’s Public Health School.

According to Sobsey, effective household treatment methods include chlorine solutions; ceramic filters; solar disinfection (in which both the heat and sunlight’s UV radiation play a role); and commercial tablets that contain both chlorine and an agent that causes water impurities to settle and be filtered out.

“The reality is that delivering safe piped water in developing countries has not been widely achieved despite decades of effort,” says Sobsey, who examines various methods of water treatment and storage for WHO. “We need alternative approaches and these are very effective.” He adds that these methods reduce household diarrheal disease, including cholera, by about 50 percent on average.

The U.S. Centers for Disease Control (CDC) is among the agencies funding one of the most promising and practical home-treatment methods—a locally produced chlorine bleach solution coupled with safe storage containers. Projects to provide health education and market the bleach product are underway or planned in 19 countries.

The bleach solution can provide safe water for a penny or less per day for a household of six, and the CDC is currently exploring whether the method can be economically self-sustaining. The agency is also examining whether treated water can make infant formula safer for babies of HIV-infected mothers who choose not to breastfeed to reduce the risk of HIV transmission.

Paola Scommegna is a freelance writer.

For More Information

David Cutler and Grant Miller, “The Role of Public Health Improvements in Health Advances: The Twentieth-Century United States,” Demography 42, no. 1 (February 2005): 1-22

Mark D. Sobsey, “Managing water in the home: Accelerated health gains from improved water supply,” (Geneva: World Health Organization 2004), accessed online at www.who.int/water_sanitation_health/dwq/wsh0207/en on May 2, 2005.

United Nations Children’s Fund (UNICEF), State of the World’s Children 2004, accessed online at www.unicef.org/sowc04 on May 2, 2005.

UNICEF and World Health Organization (WHO), “Meeting the MDG Drinking Water and Sanitation Target” (2004), accessed online at www.unicef.org/wes/mdgreport on May 2, 2005.

WHO and UNICEF, Global Water Supply and Sanitation Assessment 2000 Report (Geneva: WHO, 2000).