The Water Quality and Health Council is an independent,
multidisciplinary group sponsored by the Chlorine Chemistry Council. Its mission is to promote science based practices and policies to enhance water quality and health by advising industry, health professionals, policy makers and the public.

Drinking Water & Health Newsletter
June 1, 1993

Table of Contents

Risk and Risk Perceptions
By Bruce Bernard

The Drinking Water Blues
By Joan Rose

"Reg-Neg" Rules Would Have Major Impact on Water Treatment Facilities

What Are Disinfection By-Products?

Treatment Techniques For Minimizing Disinfection By-Product Formation

Cholera Update

Risk and Risk Perceptions
by Bruce Bernard
SRA International, Inc.

How often have you been asked questions such as, "how safe is this medication?" or how dangerous is skiing?," or, more importantly, "how safe is our drinking water?" At the heart of these questions is a recurring theme: risk. Risk has become an important concept for those concerned with public health, particularly those charged with ensuring the delivery of safe drinking water. The public today has a heightened sense of risk. Those of us in the public health community, therefore, need to understand the processes that contribute to public perceptions of risk, so we can communicate effectively.

What is Risk?

The term "risk" may mean significantly different things to different people. For this discussion, risk is defined as encompassing both the likelihood of something negative occurring and the consequences of that occurrence. For example, if thunderstorms are a common occurrence in community X and thunderstorms in community X typically result in significant damage, then the risk of damage during the next thunderstorm will be high.

Risk assessment is a field of scientific research dedicated to defining and measuring risk. Risk assessors calculate the likelihood of particular events resulting in a specific consequence. The event/consequence may be demonstrable or theoretical. If demonstrable, the event/consequence has occurred before and one can calculate the likelihood that it will happen again by reviewing documented evidence, such as, one of every five thunderstorms in community X has resulted in significant damage.

Calculating the likelihood of an occurrence based on a theoretical assumption can be even more complex, though typically resulting in minute probabilities. How likely is it that a terrorist will steal a nuclear missile and point it at the United States? The fact that many Americans may be afraid of this particular scenario illustrates that extremely minute risk probabilities do not always translate into a public perception of minimal risk. This situation also can be illustrated by examining current debates over the safety of our drinking water. Recent concerns over theoretical health risk posed by drinking water disinfection by-products (DBPs) have raised fears about the safety of tap water. This has occurred despite the fact that drinking water disinfection has for years provided U.S. citizens with the safest drinking water in the world protecting citizens from the demonstrated risk of waterborne disease.

At issue in the drinking water debate is an assessment of the relative risk of two different circumstances the demonstrated risk of waterborne disease and theoretical risk of disinfection by-products. The process of making such an assessment is known as comparative risk analysis.

Comparative Risk

For years, regulators and risk assessors have evaluated risk based on a risk-to-benefit analysis (i.e., does the benefit outweigh the risk). However, in many instances the benefits are not quantifiable, are unknown, or are based upon an individual's personal values. Since risk cannot be eliminated but only replaced by other hopefully lower risks, a different type of analysis is more realistic. Approximately 15 years ago, I coined the term Comparative Risk for the process of comparing one risk to another (i.e., which risk is lower given approximately equal or unquantifiable benefits)? For example, when we cross the street, we quickly compare the risk of jaywalking with the risk of losing our jobs if we are late for a meeting. When evaluating a situation based upon comparative risk, we seek to find a balance between two risks: If I'm late for this meeting I will lose my job, so I will jaywalk. But I'm going to wait until that speeding bus passes before I run across the street. Comparative risk analysis also plays a major role in the drinking water debate.

Water treatment facilities across the country have a responsibility to ensure the delivery of safe drinking water. Each day these facilities seek and find a balance that minimizes both the risk of waterborne disease and the risk of disinfection by-products. However, much of the public does not understand this concept. Many argue that disinfectant levels should be lowered to achieve better control of the remote risk of disinfection by-products even though the scientific community warns such a move could drastically increase the demonstrated risk of waterborne disease. Why does the public nevertheless grow anxious? Because, as discussed above, remote probabilities of risk do not always translate into a public perception of minute risk.

Perceived Risk, Actual Risk and Acceptable Risk

As the drinking water debate illustrates, perceived risk is often very different from actual risk. Risk anxiety levels are not directly proportional to actual risk probabilities. Emotions and cultural values often play a major role in distorting abstract scientific facts. And risk assessors tell us that most individuals find self-imposed or self-controlled risks (such as jaywalking) to be less risky. Familiar, detectable and natural risks also are included in the category of tolerable risk.

Conversely, risk assessors also tell us that circumstances perceived as involuntary, new, undetectable, man-made or uncontrollable are far less acceptable. Indeed, Paul Slovic, a physiologist from the University of Oregon who studies public perception of risk, notes, "Americans today feel they are at more risk from technology than ever before. Yet, in terms of health, life expectancy, and even accidents, things have improved greatly."

What confounds the dilemma of perceived risk versus actual risk is the publics' sense of outrage when they feel that the people they have trusted with their health and safety appear to be ignoring or minimizing their concerns. It does not seem to matter whether perceptions of risk are based on fact or emotion, citizens need to know that their health and safety are being protected. Blind assurances that the risk of X happening in community Y is so remote that there is no reason to worry are insufficient.

Message to Our Readers

All of us in the public health community have an obligation to understand and care about the concerns of our publics. Perceptions of risk are not always based upon demonstrated evidence but rather emotion and societal values. Whatever they are based on, the concerns of your constituents must be addressed in a manner that reassures them that you share their concerns and are continually looking for better ways to safeguard their health.

Risk communication is an intriguing combination of science and emotion. The following articles will provide more information on this topic.


By Joan Rose
College of Public Health University of South Florida
Tampa, Florida

After decades of taking it for granted, drinking water received national interest when the media, the water industry and congressional leaders turned their attention to one of the largest waterborne outbreaks documented in the United States in the last decade.

Cryptosporidium, a protozoan parasite similar to Giardia, infiltrated the city of Milwaukee, resulting in nine deaths and causing between 211,000 and 400,000 cases of diarrhea. While Milwaukee wondered when their tap water would be safe to drink again, public health officials across the country were asking, will the public have confidence in the drinking water? Is our drinking water supply at risk? Could this happen in our community?

A relatively newly recognized pathogen (first identified in 1907), Cryptosporidium has caused waterborne outbreaks in the United States before: in Texas from a contaminated well (1985); in Georgia associated with a filtered surface water supply (1987), and in Oregon from springs and filtered river water (1992). Several waterborne Cryptosporidium outbreaks have been documented in the United Kingdom as well.

Researchers have learned several things from these episodes. Cryptosporidium is an intestinal protozoan and is transmitted through fecal contamination. It may originate with animals (cattle, in particular, are suspected). But the organism may also originate from human wastes and has been found routinely in waste-water. The organism's environmental life stage, the oocyst, can be commonly found in U.S. and Canadian surface waters. The greater the level of waste input from humans and domestic animals and the less watershed protection, the greater the concentrations of oocyst.

During an outbreak, some significant contamination event apparently overwhelms the drinking water treatment system. In Milwaukee, domestic waste-waters and animal waste discharge into the Milwaukee River, which, in turn, discharges into Lake Michigan, very likely contributing to the contamination. At the treatment facility, the situation was exacerbated by less-than-optimal coagulation and filtration, as well as by recycling the backwash waters from the filters. These circumstances, in addition to changes in the removal efficiency of the filters, left the population of Milwaukee vulnerable to Cryptosporidium, previously an unrecognized threat.

Minimize Risk

Many utilities and communities throughout the United States and Canada face a similar risk. What can be done? There are three important and interdependent components in the process of producing safe water (1) source protection, (2) filtration and (3) disinfection.

Source protection

  1. Steps already have been initiated to evaluate potential sources of Cryptosporidium in surface supplies which may be amenable to a prevention control. The American Water Works Association has recommended that water supplies be tested for the oocyst. This data will help decision makers evaluate sources, and take into account the seasonal water quality changes which may contribute to contamination events.


  1. While filtration is an effective step for the removal of the oocyst, optimization and treatment reliability must be maintained.


  1. Finally, no single disinfectant will control this protozoan. In the aftermath of the Milwaukee incident, ozone was mentioned as a possible alternative to chlorine; however an outbreak of Cryptosporidium recently occurred in Ontario, Canada, where ozone was used as a pre-disinfectant. Additionally, if ozone is used, it must be used in tandem with another disinfectant such as chlorine or chloramine because ozone does not provide a residual disinfectant level. Together, this dual disinfectant barrier could be very effective against most microbial contaminants.

Despite having the safest tap water in the world, contaminants such as Cryptosporidium have occurred in U.S. and Canadian drinking water supplies. Those of us responsible for protecting public health and providing safe drinking water must rise to meet this latest challenge: to prevent future Cryptosporidium outbreaks and to assure the safety and integrity of our nations' drinking water.


The Regulatory Negotiation (Reg-Neg) committee established by EPA to negotiate and propose a new rule setting limits for drinking water disinfectants and disinfection by-products has reached a tentative agreement that may if implemented, encourage water treatment facilities to move away from chlorination, the nation's primary drinking water disinfectant for the past 80 years.

Safe Drinking Water Act

Under the Safe Drinking Water Act (SDWA), EPA is required to establish new standards for drinking water contaminants; drinking water disinfectants and disinfection by-products are considered contaminants for the purpose of this rulemaking. Disinfection by-products sometimes form as a result of a reaction between drinking water disinfectants and organic matter (referred to as organic precursors) that occur naturally in many water sources.

However, some of the recent outcomes of the Reg-Neg process are highly controversial. In fact, the National Rural Water Association, one of five water industry groups invited to participate in the negotiations, recently withdrew from the Reg-Neg process because of the lack of science-based evidence in support of commit- tee recommendations.

The lack of supporting scientific evidence is most noticeable when reviewing the details of the committee's proposed phase two recommendations. Phase two calls for drastic reductions in maximum contaminant levels (MCLs) which, if implemented, would require a major overhaul in the nation's water-treatment infrastructure. If the message being sent to the water industry is that a major overhaul is required, documented evidence should clearly show that such an overhaul is both necessary and beneficial.

Two-phase Implementation

The proposed disinfectant/ disinfection by-products rule would be implemented in two phases. Phase one of this rule would lower MCLs for chlorination by-products known as trihalomethanes (THMs) from 100 parts per billion (ppb) to 80 ppb by 1997. At the same time, phase one would establish a 60 ppb MCL for previously unregulated chlorination by-products known as haloacetic acids. Phase one of the proposed rule also would establish maximum residual disinfectant levels (MRDLs) for chlorine and chlorine-based disinfectants.

Additionally, the first phase of the rule would require large water systems (those serving more than 100,000 people) over the next several years to conduct raw (untreated) water monitoring for microbial contaminants and a range of disinfection by-products in treated water. To address unknown disinfection byproducts from all disinfectants, organic carbon precursor removal will be required if total organic carbon (TOC) of the finished water is greater than 2.0 mg/l.

If implemented, certain phase one requirements would apply to both large and small water systems. Phase one compliance costs are estimated to be in the range of $3 billion in capital, and over $400 million in annually recurring operating and maintenance expenses.

Phase Two

The proposed disinfectant/ disinfection by-products rule (effective in the year 2002) specifies further lowering of MCLs to 40 ppb for total THMs (TTHMs) and 30 ppb for haloacetic acids. The stringent MCLs established in phase two, referred to as a "backstop," will automatically become law unless the second regulatory negotiation (REGNEG 2), which will occur in 1998-99, reaches agreement on some other levels. The Chlorine Institute, which has been represented on the RegNeg Technologies Work Group, has objected to the phase two recommendations.

Clearly, both phases of the disinfectant/disinfection byproduct rule proposed by the Reg-Neg committee would have a significant impact on water utilities throughout the United States. The new rule would be expensive and may require the adoption of alternative water treatment technologies. Many of these alternative technologies may have adverse public health and environmental impacts of their own. For example, ozonation is seen by some as a viable alternative to chlorination. However, in water sources containing bromide, ozone forms byproducts known as bromates, which scientists recognize as a far more significant health risk than THMs or haloacetic acids. In addition, ozone breaks down quickly and does not provide disinfection through the water system to the tap.

It is vital that all concerned with the nation's public health take steps to ensure that the final disinfectant/disinfection by-products rule be based on sound science and reflective of logical and attainable public health benefits.

All interested parties should be sure to comment on the proposed rule, which is expected later this year. For more information on the RegNeg process, contact the U.S. EPA Safe Drinking Water Hotline at 800-426-4791.


Drinking water disinfection has been, and continues to be, one of the most important public health measures of the 20th century, having greatly reduced the threat of waterborne disease in the United States, Canada and other developed countries. Over the past 20 years researchers have been looking at the by-products of reactions between drinking water disinfectants and organic matter that exists naturally in many water sources. Resulting compounds are commonly referred to as disinfection byproducts.

Increased media coverage of disinfection by-products, paired with a heightened sense of risk amongst the general public, has caused more people to ask about the safety of the nation's drinking water. (See related story on Perceptions of Risk). Most often, they look to the nation's public health community for answers.

While the body of science regarding these issues is inconclusive, those responsible for the nation's public health and the safety of its drinking water must be able to accurately respond to constituents questions about these issues. The following overview should help.

How Are Disinfection By-Products Formed?

When raw water (from a lake, stream or other untreated source) enters the water treatment system, it typically carries organic materials it picked up along the way, such as decaying vegetation and animal wastes. Some of these materials serve as organic precursors and react with disinfectants during the treatment process, forming disinfection by-products. These by-products occur more frequently in the summer, when the level of organic material in raw water typically is higher, and water temperatures generally increase.

Disinfectants also can react with other naturally occurring constituents in raw water, such as the bromide ion, to form bromine-based or brominated disinfection by-products (see chart below).

Disinfection By-Products - Formation Potentials1 Assessing Potential Human Health Risk

Source Water Characteristics




Chlorine Dioxide

Natural Organic Materials

Trihalomethanes, halocetic acids, aldehydes

Aldehydes, ketones

Cyanogen chloride

Chlorate ions, chloride ions

Bromide (from sea awater, oil field brine or geological weathering of minerral deposits)

Bromoform, dichlorobromomethane

bromate, bromoform

Does not oxidize bromide

Does not oxidize bromide

Inorganic compounds (Iron, manganese)

Forms insoluble compounds

Forms insoluble compounds

Does not oxidize inorganics

Residual chlorite, minimal quantities of chlorate

Other Factors that Affect By-Product Formation

1Disinfection by-products occur from a reaction between disinfectants and certain source water characteristics. This chart identifies by-products from different disinfectants and source water characteristics.

Several other source-water characteristics affect the quantity and type of disinfection by-products that may form during the disinfection process. They include:

  • Coloration
    If sourcewater is highly colored, there is a greater chance for formation of trihalomethanes

  • pH value
    Acidic pHvalues typically contribute to higher formations of haloacetic acids; alkaline pH values contribute to higher formations of trihalmethanes

  • Temperature
    Warmer source waters tend to have higher by-product formation potential

Assessing Potential Human Health Risk

Disinfection by-products were first identified in the early 1970s. Much of this research has focused on chlorination by-products since chlorine is used in some form by over 95 percent of water systems in the United States. This research has been enhanced by the development of sophisticated laboratory techniques that can measure chlorine compounds in water in parts-per-billion and even parts-per-trillion. Likewise, these techniques have raised questions about other disinfectants, which also create byproducts. However, the body of knowledge about by- products from alternative disinfectants, such as ozone, is incomplete.

Trihalomethanes, or THMs, are a class of chlorinated organic compounds that sometimes form as a result of the chlorination process. Early studies suggest that these compounds are carcinogenic to certain laboratory animals at levels much higher than commonly found in drinking water. Many studies have been undertaken to determine whether THMs constitute a human health risk.

In 1990, the International Agency for Research on Cancer (IARC), an arm of the World Health Organization, assessed the strength and reliability of virtually every major scientific analysis of the potential health effects of chlorinated drinking water. They found that chlorinated drinking water was not a classifiable human carcinogen.

Moreover, various procedures exist to remove organic materials from water during the treatment process, thereby reducing disinfectant byproduct formation (see related story).


Treatment techniques are available that provide water suppliers the opportunity to maximize drinking water safety and quality while minimizing the risk of disinfection by-product formation. Disinfection by-products typically form as a result of a reaction between naturally occurring organic matter in raw or untreated water and drinking water disinfectants.

One of the best methods to control disinfection by-products is to remove the organic precursors prior to disinfection. Other conventional methods include changing the point of chlorination and lowering chlorine feed rate. An October 1991 American Water Works Association (AWWA) Water Quality report identified effective procedures for reducing the formation of disinfection by-products, as follows:

Organic Precursor Removal

There are three ways to effectively remove organic precursors:

Coagulation and Clarification
Most treatment plants use the coagulation process to remove as much sediment as possible. Coagulation processes can, however, be used effectively for natural organic matter removal. Precursor removal is possible when aluminum or ferric salts are used as coagulants for sediment control. Further precursor removal is achieved by reducing the pH prior to or during the addition of these coagulants.

A recent study by Reckhow and Singer (Reckhow, David A., and Philip Singer, Chlorination By-Products in Drinking Waters: From Formation Potentials to Finished Water Concentrations) notes that alum coagulation "has long been known as an effective means of removing natural organic matter." The study also states that alum coagulation is effective for removing organic precursors. Numerous studies show that ferric salts also are very effective.

Adsorption processes have been used successfully in some applications for removing disinfection by-product precursor material. Activated carbon historically has been used to provide adsorption both granular activated carbon and powder activated carbon are available for this function.

Membrane Technology
Historically, membranes have been used for desalination of brackish waters. One process, which uses pressure to force the liquid through a membrane, has proven particularly successful in removing disinfection by-product precursors. The AWWA report states that membrane procedures "actually remove precursors from the finished product, which makes it a promising alternative for future control of disinfection byproducts."

Conventional Treatment Optimized for Disinfection By-Product Removal

There are two ways to optimize conventional treatment:

Change the Point of Chlorination
According to the AWWA Water Quality Committee report, "one of the simplest solutions for the reduction of THM formation is the movement of the first point of chlorine application to as late in the treatment process as possible." By moving the point of chlorination to late in the process, most organic precursor materials will be removed before the water is chlorinated, thus minimizing disinfection by-product formation potential.

Lower the Chlorine Feed Rate
By lowering the rate at which chlorine is applied to water, there is less tendency for the organic precursors to react with chlorine, thus reducing the potential for byproduct formation.


World Health Organization Reports "No End in Sight" for Global Cholera Epidemic

An additional 131, 000 cases of cholera including 2,265 deaths, have been reported so far in 1993 and the epidemic shows no signs of abating, the World Health Organization (WHO) recently reported.

More than half of these new cases were reported in Peru and approximately 44,000 were reported in four African countries Malawi, Mozambique, Zambia and Zimbabwe.

A new cholera bacteria has been found on the Indian subcontinent and is likely to spread, according to WHO.

The ongoing epidemic has ravaged Latin America and Africa since 1991, resulting in over 600,000 cases of cholera and 7,000 deaths.

Drinking Water & Health Newsletter is a Publication of the Public Health Advisory Board to the Chlorine Chemistry Council


Safe Water Advisory Committee

Sanford M. Brown, Jr.
School of Health and Social Work,
California State University, Fresno

Bruce K. Bernard, PH.D.
SRA International
Washington, DC

Linda Golodner
National Consumer League
Washington, DC

Ralph Morris
Galveston County (Texas)
Health District

Fred Reiff
Pan American Health Organization
Washington, DC

Chlorine Institute


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