Water & Health Newsletter
Table of Contents
The ability to continue delivering safe drinking water is a constant challenge to water suppliers. The news media, government regulators and the public have focused attention on an array of problems - from crumbling infrastructure to contaminated source water to the presence of disease-causing microbes. Both the cause and result of some of these problems center on whether the pipes in water distribution systems are well maintained and kept free of deposits that can harbor a variety of contaminants.
Deposits on the interior walls of the pipes in water distribution systems stem primarily from two processes. Biofouling is the development of an organic film (biofilm) composed of microorganisms and their secretions. Deposits also can be a result of chemical reactions such as the precipitation of substances that are dissolved in the water, sedimentation of suspended matter and corrosion of the pipe material.
Biofilms have recently received considerable news coverage. In Washington, DC, during the spring of 1996, E. coli was found during routine sampling of the water distribution system and remained present for some time after initial corrective measures were taken. Biofilm was cited as the primary cause of this contamination, as exhibited in a heavily encrusted pipe sample shown on television news reports.
Even though it was suggested that biofilm presents a new threat to human health, the water supply and public health sectors have long recognized that biofilms are present to some degree in almost every water distribution system. When conditions sufficiently restrict its growth, biofilm causes few problems. However, when growth is uncontrolled, biofilm can cause serious problems, including a decrease or depletion of the chlorine residual that increases contamination risks further out in the distribution system, as well as increased bacterial counts and bacterial regrowth in the distribution system. For these reasons, uncontrolled biofilm presents a significant threat to public health.
Microbial regrowth and biofilm formation
The water-pipe interface is the location at which almost all the growth of microorganisms takes place. Very little growth takes place in the water flowing through the pipes due to the water's short residence time in the distribution system and its exposure to residual chlorine.
The formation and accumulation of biofilm on the pipe walls is influenced by a number of factors:
Biofilms can be composed of many different organisms. The species present in biofilms will vary in both place and time, depending upon the nutrients and amount of oxygen present in the water, the seed microorganisms, the temperature and pH of the water, and the pipe material. The three principal nutrients essential for biofilm formation are assimilable organic carbon (AOC), nitrogen and phosphorus.
The entrance of seed microorganisms is necessary to initiate biofilm growth. Bacteria are nearly ubiquitous in the aqueous environment and are usually present in limited numbers in water leaving the treatment plant. If conditions in the distribution system are suitable, bacteria will quickly multiply in the biofilm. Also, coliform organisms (including E. coli) and various waterborne pathogens can enter the system from external sources during pipe construction or repairs, at times of inadequate water treatment, from back siphonage and cross connections, from inadequately protected storage tanks and reservoirs, and take up residence in the biofilm.
Control of biofilm
Chlorination is the principal means of controlling biofilm fouling in water distribution. In water systems where there are few nutrients for microbiological growth and the water is chemically stable, the normal chlorine residual is sufficient to keep biofilm under control. However, where the water is nutrient rich and the biofilm has developed a protective coating over a period of time, it is necessary to apply chlorine at higher levels and flush the system with high-velocity flow to obtain sufficient shear force and turbulence to remove the biofilm from the system.
The transport of the chlorine to the biofilm is influenced by the concentration of chlorine in the water and the turbulence of the water. An increase in the water's turbulence will both increase the availability of chlorine at the interface and increase the fluid shear forces that can physically loosen and remove the biofilm, thereby exposing more biofilm surface to chlorine.
The pH value also is important in dislodging biofilm, with detachment occurring much more rapidly at higher pH values.
Biofilm in some parts of the distribution system may be controlled simply by maintaining the normal chlorine residual, whereas other parts may require special efforts such as superchlorination and high-velocity flushing on an intermittent basis to achieve control. In extreme cases, scouring with mechanical devices (referred to as "pigging" the pipeline) may be necessary to remove biofilm and encrustation.
In the United States, chlorine is the principal disinfectant-oxidant used for controlling biofilm, but under adverse conditions of high AOC levels and hardened biofilm, it may not be completely effective. In weighing the use of alternative disinfectants for biofilm control, it should be remembered that disinfectants other than chlorine may interact differently with biofilms.
Experience indicates that no two biofilm situations are exactly the same and that biofilm growth and control involve complex biological and chemical interactions. In most cases, it is more expensive to remove biofilm after it has accumulated over long periods of time and has become well established than it is to routinely carry out the preventive measures to keep its growth under control. Mechanically scouring a distribution system to remove biofilm requires numerous excavations and involves service disruptions. The expense is even greater to replace distribution pipes rendered unusable because of obstructing encrustations or leakage from perforation of the pipe walls caused by bioaccelerated corrosion.
Not only are continuous maintenance of an appropriate chlorine residual and reduction of the AOC through source protection and improved water treatment practices more economical, but they also reduce water quality deterioration, public health concerns and customer dissatisfaction.
Fred Reiff, now a private consultant, retired in 1995 after 14 years with the Pan American Health Organization. Mr. Reiff is a member of the Public Health Advisory Board of the Chlorine Chemistry Division of the American Chemistry Council and an expert in international public health activities related to waterborne diseases.
"Americans do have a right to know what's in their drinking water and where it comes from before they turn on their taps."
President Bill Clinton, on signing the Safe Drinking Water Act, August 6, 1996
A new era in the area of risk communication is about to open up with the passage of the 1996 Safe Drinking Water Act Amendments. The "right to know" provision of the new Act requires public water utilities serving 10,000 people or more to mail to their customers and the media annual reports of the results of monitoring for waterborne contaminants. Small systems may comply by publishing reports in local newspapers. All systems must also issue a report within 30 days if disease-causing pathogens such as cryptosporidium are detected in drinking water supplies, requiring a boil-water advisory or other prompt action.
In addition, the Information Collection Rule, recently issued by the Environmental Protection Agency, requires large public water utilities to report the results of monitoring for both microbial pathogens and disinfection by-products to the agency. While the utilities themselves do not have to issue monitoring reports to their customers, the information may be publicly released by EPA.
These new federal requirements, coupled with public disclosure rules that already exist in some states, mean that public health and water authorities must be prepared to answer questions and translate technical data so that the public has an accurate understanding of the potential risk at hand. The challenge is clear: how to provide accurate, complete information without causing unnecessary concern or even panic in the community.
Against the backdrop of heightened public concern about drinking water safety (e.g., Milwaukee and Washington, DC), effective risk communication is not an easy task. Understanding how the public can react to information about risks provides useful insights for public health professionals and can help you prepare for community questions.
Understanding Public Perception of Risk
Experience and research in risk communication has identified the key factors in people's perception of risk. Among other characteristics, people most fear reported risks that they see as involuntary, unfamiliar and uncontrollable. They will be less concerned if they perceive risks as voluntary, familiar and controllable. Thus, in comparing these risk perceptions, a community water supply contaminated with cryptosporidium would fall into the first category whereas risky personal behavior such as drinking alcohol or smoking would fit the second.
If people drink water directly from the tap, they may have little control over its quality. Therefore, they may overreact to certain risks and ignore others. Risk communicators usually know in advance whether they are dealing with panic or apathy. Acknowledging the public's need to know and their fears - and advocating a remedy for what it views as unfamiliar or unfair - can help defuse concern.
The general public's view of risk usually is very personal. How risks are described verbally will affect risk judgments: microbial contaminants anticipated to cause acute illness in the general population are very serious. Those that might affect only a few sensitive individuals should be communicated with clarity.
Issues of fairness and the power over decision making also loom large in the public's willingness to accept risk. Communicating with the public early on will go a long way toward overcoming the fairness issue and help move along the process of what to do about the risk itself. The public should be told the facts.
Explaining risk information
Assessing risk and communicating risk assessment results to the public should take into consideration both the complexity of risk issues and how the public will receive the information presented. In general, people care more about safety than potential risk, and they want straight answers to their questions. Their most basic questions are, "What are you going to do to fix the problem?" And, "What do I have to do to protect my family from harm?"
Communicating technical and scientific information to the public means being able to explain terms such as "parts per million" and whether a contaminant presents an immediate threat, especially to children or other vulnerable populations. You should define acute versus chronic health effects and describe exposure/effect relationships. Most risk communicators rely on three standard methods for getting across technical content:
Remember that consumers should know what affects their health. That is why it is critical to involve citizens in decision making about risks in their communities.
There are numerous resources to assist water and public health authorities in devising effective risk communication strategies, including the Harvard Center for Risk Analysis; The Columbia University School of Public Health & Center for Risk Communication; Environmental Communication Research Program, Rutgers University; the U.S. Public Health Service Agency for Toxic Substances & Disease Registry; and the National Environmental Health Association (NEHA).
Sources for this article included: NEHA/Agency for Toxic Substances & Disease Registry, Materials of Workshops for Environmental Health Professionals; Explaining Environmental Risk by Peter M. Sandman (for USEPA Office of Toxic Substances, 1986); Health & Environment Digest, December 1987, April 1992, September 1995.
Safe Drinking Water Act of 1996
On August 6, 1996, President Clinton signed into law (PL104-182) the Safe Drinking Water Act (SDWA) Amendments passed by Congress on August 3rd. Enacting the first SDWA reforms in ten years culminated an effort that had occupied the past two Congresses.
Some of the bill's major provisions were previously reported (Drinking Water & Health, Summer 1996), and they remained essentially unchanged during consideration by the House-Senate conference committee. A number of key amendments relating specifically to drinking water and public health concerns are summarized below:
Other provisions of the new SDWA Amendments add controls on lead pipe fittings, fixtures and solder; require estrogenic screening of chemical substances found in drinking water; establish a new source water protection program; authorize a State Revolving Loan Fund and infrastructure grants to help states fund water system improvements; and direct EPA to develop regulations for groundwater disinfection, arsenic, radon and sulfate.
The bill also authorized funding for grants to help border states improve drinking water supplies and wastewater treatment in the Colonias (see report in Drinking Water & Health, Winter 1996).
Zebra Mussels. Congress passed the National Invasive Species Act, which provides guidelines for maritime management of ship ballast to prevent introduction of "nonindigenous species" (zebra mussels) into the Great Lakes and encourages the development of prevention technology at water treatment facilities.
Miscellaneous. Congress failed to complete action on regulatory reform, reauthorization of the Clean Water Act and Superfund legislation.
Central Arizona Project pilot aquifer recharge plan
A pilot aquifer recharge effort by the City of Tucson began operations in August 1996 to restore high-quality drinking water to the people of Tucson, meet long-range water supply needs and replenish Tucson's overdrafted groundwater supply.
In 1992, the City of Tucson Water Department began supplying customers with treated Central Arizona Project (CAP) surface water rather than groundwater. Subsequent consumer complaints about rust-colored, smelly or corrosive water led to the passage of a citizens' initiative - the Water Consumer Protection Act - in November 1995, which prevents the delivery of CAP water directly to customers unless it meets certain water quality standards and establishes methods for CAP water use.
CAP brings 1.5 million acre-feet* of water each year from the Colorado River at Lake Havasu, in western Arizona, into central and southern Arizona, where the water is treated and delivered to the Phoenix and Tucson metropolitan areas. Designed to supply renewable Colorado River water for agricultural, industrial and municipal use in order to reduce reliance on groundwater, CAP consists of a 335-mile water delivery system of canals, tunnels, pipelines and pumping plants.
Before the introduction of CAP water in November 1992, the Tucson Water Department relied on groundwater to service more than 600,000 customers. The need for CAP water is based on Tucson's groundwater being used two-and-a-half times faster than it can be replaced by nature. By the year 2006, the Tucson Water Department will serve up to 700,000-800,000 customers.
Under the aquifer recharge project, CAP water will be released into man-made basins to percolate naturally through the earth until it reaches the underground water table.
Specially designed wells will be constructed to recover the water, treat it with chlorine at the source and deliver it to Tucson Water customers.
The six-month pilot phase will determine how fast CAP water can percolate into the aquifer, how much water can be stored underground, water recovery capability and the impact on local groundwater quality. The project could become permanent and recharge up to 100,000 acre-feet per year. Early monitoring showed that water was sinking in at more than one foot per day.
The total cost of the project is approximately $56 million, which includes construction of the reservoir, the recharge basins, 11.5 miles of pipeline and an estimated 25 high-capacity wells. The project will not be fully operational for at least three years.
For more information, please contact the Tucson Water Department Public Information Office at (520) 791-4331.
* An acre-foot is the amount of water that would cover an acre to the depth of one foot and equals 325,851 gallons.
An increase of reported cholera cases worldwide since 1991 has led government health experts to warn doctors to be prepared to diagnose, treat and investigate cases of cholera. A study by the National Center for Infectious Diseases said there were 160 cholera cases reported in the U.S. and its territories from 1992 to 1994, compared with 136 reported in the previous 26 years. Virtually all cases reported in the U.S. are related to travel or immigration.
While reports of these cases are a concern to U.S. public health officials, the historic reliance on chlorine disinfection of drinking water supplies in North America has helped protect our population against cholera and many other infectious waterborne diseases.
Since the onset of the Latin American cholera epidemic in 1991, the number of cholera cases reported in the U.S. has increased dramatically. From 1965 to 1991, an average of five cases per year were reported - 31% acquired abroad. From 1992 to 1994, the average was 53 cases per year, and 96% were travel associated.
More than one million cases of cholera and 10,000 deaths have occurred in Latin America since the onset of the epidemic. West Africa has reported 42,500 cases of cholera in the first nine months of 1996, a sixfold increase in the region since 1993. In Southeast Asia, more than 200,000 people were infected in the early 1990s. The increase in cholera in the U.S. is largely due to the greater number of international travelers. The study recommends that persons who are traveling in cholera-affected areas minimize their risk of infection by selecting low-risk foods and beverages and avoiding food and drinks from street vendors. Cooked foods should only be eaten hot. Fruits and vegetables eaten raw should be peeled.
Low-risk beverages include those that are hot, those that are carbonated served without ice, and boiled or chemically disinfected water.
Cholera is a disease caused by infection of the small intestine by certain strains of the bacteria species Vibrio cholerae. In severe cases, it can produce profuse diarrhea, severe dehydration, loss of essential salts and death within hours. It is spread by contaminated water, raw or undercooked seafood or other contaminated food. Symptoms include watery diarrhea, cramps, nausea, vomiting and shock. Secondary transmission occurs in areas that lack adequate sanitation and safe drinking water and is often associated with substandard hygiene.
The mainstay of cholera treatment is rapid oral rehydration and, in severe cases, intravenous fluids. Treatment with antibiotics may shorten the duration of diarrhea but does not cure the disease. Vaccines are available but not recommended because they are less than 60% effective and offer protection for only three to six months. Also, they do not help control the spread of the disease.
Many cases of cholera in the U.S. may go undetected by physicians who are unfamiliar with the disease. Physicians who treat patients for severe watery diarrhea should order a stool culture to test for the presence of the bacteria in the feces. Cases of cholera should be reported to local and state health departments.
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