Chlorination has played a critical role in protecting America's drinking water supply from waterborne infectious diseases for 90 years. The filtration and disinfection of drinking water has been responsible for a large part of the 50 percent increase in life expectancy in this century. That fact led Life magazine to recently cite the filtration of drinking water and use of chlorine as "probably the most significant public health advance of the millennium."

One of the first known uses of chlorine for water disinfection was by John Snow in 1850, when he attempted to disinfect the Broad Street Pump water supply in London after an outbreak of cholera. In 1897, Sims Woodhead used "bleach solution" as a temporary measure to sterilize potable water distribution mains at Maidstone, Kent (England) following a typhoid outbreak.

Continuous chlorination of drinking water began in the early years of this century in Great Britain, where its application sharply reduced typhoid deaths. Shortly after this dramatic success, chlorination was begun in Jersey City, N.J., in 1908. Adoption by other cities and towns across the US soon followed and resulted in the virtual elimination of waterborne diseases such as cholera, typhoid, dysentery and hepatitis A. Before the advent of chlorination for drinking water treatment, typhoid fever killed about 25 out of 100,000 people in the US annually, a death rate approximating that currently associated with automobile accidents.

Chlorine-based chemicals have been the disinfectants of choice for treating drinking water for nearly a century. In fact, some 98 percent of systems that treat water employ chlorine-based disinfectants. More than 200 million Americans and Canadians receive chlorine-disinfected drinking water every day.

Chlorine's most important attributes are its broad-spectrum germicidal potency and persistence in water distribution systems, providing residual protection against microbial regrowth. It also is used to control taste and odor problems by oxidizing many naturally occurring substances such as foul-smelling algae secretions, odors from decaying vegetation, hydrogen sulfide and ammonia.

Public Health Protection

Chlorinated drinking water's chief benefit is the protection of public health through the control of waterborne diseases. It plays a paramount role in controlling pathogens in water that cause human illness, as evidenced by the virtual absence of waterborne diseases such as typhoid and cholera in developed countries.

Untreated or inadequately treated drinking water supplies remain the greatest threat to public health, especially in developing countries, where nearly half the population drinks contaminated water. In these countries, diseases such as cholera, typhoid and chronic dysentery are endemic and kill young and old alike. In 1990, over three million children under the age of five died of diarrheal diseases. Unfortunately, the availability of safe drinking water in many areas is practically nonexistent, due to poverty, poor understanding of water contamination, and lack of a treatment and delivery infrastructure.

International assistance groups, including the World Health Organization and the Pan American Health Organization (PAHO), have long-standing technical assistance and education programs to improve water supply and sanitation practices. It has been estimated that such improvements - including chlorine disinfection - can prevent 25 percent of all diarrheal outbreaks and reduce childhood mortality by equal levels.

A recent example of the continuing public health threat from waterborne disease outbreaks occurred in Peru in 1991, where a major causative factor was the absence or inadequacy of drinking water disinfection. This failure to disinfect was partly based on concern about U.S. reports on disinfection by-products. The result: a five-year epidemic of cholera, its first appearance in the Americas in this century. The epidemic spread to 19 Latin American countries and has been only partially abated through public health interventions supported by PAHO's advice and technical assistance. Nearly a million cases and 10,000 deaths have been reported.

These statistics strongly reinforce the concept that water disinfection must be a primary tool in protecting public health worldwide. As noted by the American Academy of Microbiology, "The single, most important requirement that must be emphasized is that disinfection of a public water supply should not be compromised."

At the 1992 First Intemational Conference on the Safety of Water Disinfection, several researchers described the costs associated with microbiological disease as well as the benefits of illness avoided through water treatment. Real health care savings can be realized from preventing and eliminating microbial contamination in drinking water supplies.

In his conference presentation, Dr. Pierre Payment of the University of Quebec stated that the "social cost of 'mild' gastrointestinal illness in industrialized countries is several orders of magnitude higher than costs associated with acute hospitalized cases."

For example, in the United States, annual costs were estimated to be $9.5 billion (1985 dollars) for cases with no consultation with a physician, $2.7 billion for those with consultations, and only $760 million for those requiring hospitalization.

Dr. Payment presented data estimating that in 1985, about 500,000 hospitalizations and 3,000 deaths were due to gastrointestinal illnesses in the United States, the majority being of unknown origin. His study assumed that these numbers are grossly underestimated due to unreported or unidentified illnesses. Over 13 percent were due to viral illnesses, 4.9 percent were bacterial and 1.1 percent were parasitic. About 80 percent were presumed noninfectious. One out of ten deaths from gastroenteritis could be due to viruses.

Commenting on Dr. Payment's report, the American Academy of Microbiology noted, "A decrease in morbidity and mortality is not the only benefit which should be considered in a cost-benefit analysis . . . The benefits of microbiologically safe water go beyond the absence of disease, and affect the productivity of industry, as well as the prices of goods and services."

At the same conference, a paper by Gunther F. Craun et al. discussed the cost-effectiveness of water treatment for pathogen removal. An evaluation of five pathogens and treatment costs shows the favorable economic benefits of preventing infectious waterborne diseases. These benefits were determined based on an annual probability of illness and death, assuming no water treatment, and a cost of $3,000 per illness and $500,000 per death.

The report concluded that "municipal water systems designed to prevent waterborne infectious disease are one of the most effective investments of public funds that society can make. Even conservative estimates under worst-case conditions show benefit-cost ratios of 3:1 for small systems and 8:1 for large systems. Pathogen-free drinking water is a bargain."

Regarding comparison of these benefits with potential cancer risks associated with drinking water disinfection, the group noted that the costs of preventing the relatively small carcinogenic risks may not be warranted in light of many other public health risks that should be reduced.

The Future of Chlorine Disinfection

The disinfection byproducts debate has led some people to think that chlorine's use in drinking water treatment will diminish. This is highly unlikely. Other disinfectants also produce byproducts. There are other more appropriate ways to reduce disinfection byproducts such as precursor removal technologies that will not produce new disinfection byproducts.

Furthermore, chlorine is the disinfectant of choice for drinking water for a number of reasons. Its wide range of benefits can not be provided by any other single disinfectant. Chlorine-based disinfectants are the only disinfectants that provide a residual in the distribution system. This residual is an important part of the multibarrier approach to preventing waterborne disease. The increasing need for groundwater systems to disinfect may actually increase the use of chlorine for drinking water disinfection.

According to the World Health Organization, disinfection by chlorine is still the best guarantee of microbiologically safe water (WHO Regional Office for Europe, Drinking Water Disinfection). This is unlikely to change in the near future.

About the Author: Keith Christman is Director of Disinfection and Government Relations at the Chlorine Chemistry Division of the American Chemistry Council. Christman has managed disinfection issues at Chlorine Chemistry Division of the American Chemistry Council for over two years following five years as an Economist for the American Chemistry Council. He has a Masters of Science in Economics from the University of Delaware.

WaterWorld
September 1998