January 2004: Volume 46, Number 1
Do We Need Drinking Water Treatment at the Tap? -- A Rebuttal to the WET Study
by Kelly A. Reynolds, MSPH, Ph.D.
A recent survey of a well-operated public water supply system and its consumers indicates that tap water is safe. The researchers further state that point-of-use (POU) treatment offers no additional protection against waterborne disease. Don’t close up shop yet, though, as there’s more to this story.
Remember when nutritionists and health advisors recommended a diet high in salmon, a food rich in those healthy, long-chain, omega-3 fatty acids? Not long after many acquired the taste, that advice was modified via rising risks of mercury and PCB contamination. With both sides of the salmon story getting large-scale media attention, consumers were left wondering which risk was higher--eating salmon or not? And, by the way, how much is too much, or too little? The debate continues with tuna.,
Similar is the confusion in the water treatment industry. Not only do in-home purification systems improve the taste and smell of tap water, but we have sound scientific research showing that their use can decrease your amount of gastrointestinal illness by up to 40 percent or more., Then again, we also have sound scientific evidence that they don’t.
Evaluating tap water quality
In response to the 1996 Amendments of the Safe Drinking Water Act, a Congressional mandate was issued aimed at evaluating the risk of tap water. Part of this mandate involved a year-long, $3-million study known as the Water Evaluation Trial (WET), aimed at evaluating the rate of gastrointestinal illness in persons consuming tap water vs. persons consuming treated tap water.
The study was funded by the U.S. Centers for Disease Control (CDC) and Prevention and the U.S. Environmental Protection Agency (USEPA), and involved researchers from both in addition to scientists at the University of California, Berkeley (UCB) School of Public Health. Dr. Jack Colford, a UCB professor, was principal investigator on the study.
The first task at hand was to choose a test water utility. After two years of deliberation, the Iowa-American Water Co. was chosen as the site for the full-scale home intervention trial, in part because the drinking water in this area met or exceeded all federal guidelines and safety standards. The Iowa-American Water Co.’s source water is the Mississippi River, not exactly a pristine or protected water source.
Next, more than 1,200 volunteers from 456 homes were recruited. Half of the homes were given a placebo unit while the other half were supplied with POU treatment devices utilizing one-micron filtration and ultraviolet light disinfection.
Volunteers kept weekly health diaries, tracking their drinking water consumption, and gastrointestinal illness (i.e., diarrhea, cramps, nausea, vomiting). If sickened, participants supplied stool and blood samples for analysis of microbial agents. Monitoring for total chlorine, pH, temperature, total coli-forms, HPC bacteria, and turbidity at the water treatment plant also took place.
Is tap water safe?
Results of the WET study were reported at the International Society of Environmental Epidemiology in Perth, Australia, on Sept. 26, 2003. In a nutshell, the researchers found no significant difference in gastrointestinal symptoms among those given a state-of-the art home treatment system vs. those given a placebo unit. Following the presentation, a flurry of media headlines emerged professing that plain tap water was as safe as home-treated water with respect to gastrointestinal illness. Does this data make me feel better about drinking tap water? Honestly, no.
Some of the uncertainties of this study are that only a single water system was evaluated. The Iowa-American Water Co. is reported to be one of the best in the country, utilizing conventional filtration and a combination of chlorine and chloramine disinfectants. In fact, during the course of the study, the plant effluent always surpassed all water quality standards. Additionally, the study included intensive monitoring of the distribution system water quality and pressures indicating high quality delivery of the finished product.
Furthermore, the utility is a member of the Partnership for Safe Water, a voluntary cooperative effort between the USEPA and water utilities to improve water quality in the United States, exceeding federal guidelines for drinking water. Only 2 percent of the nation’s utilities using surface water sources are enrolled in the partnership for safe water.
Questions remain as to how applicable the findings of this study are to other utilities in the country that don’t exceed federal safety standards. In 1994, the USEPA determined that 30 million people--12 percent of the U.S. population--received drinking water in violation of at least one of the public health standards.
In addition, the study was limited to healthy people and, thus, no conclusions can be drawn regarding the value of POU water treatment for the 20-25 percent of Americans with compromised immune systems. POU water treatment has the potential to be very beneficial to immunocompromised populations, where microbial infection rates and outcome severity are often higher than in healthy populations.
Risks of tap water
A comprehensive review of outbreaks in drinking water systems from 1991-1998 found 126 outbreaks, 429,021 cases of illness, 653 hospitalizations, and 58 deaths reported in public and individual water systems in 41 states and three U.S. territories. Primary causes of outbreaks included contamination of untreated groundwater, inadequate disinfection of groundwater and distribution system deficiencies, especially cross-connections and corrosive water. Very few of the systems involved exceeded the USEPA’s total coliform standard in the 12 months prior to the outbreak.
More recently, greater than 28 percent of the 39 reported drinking water outbreaks in the United States from 1999-2000 were associated with community systems. Nearly half (45.5 percent) of these were due to treatment deficiencies, while another 45.5 percent were due to problems in the water distribution system.
In a 2001 report on the nation’s infrastructure, the USEPA acknowledges the need for significant investment in installing, upgrading or replacing infrastructure for delivering safe drinking water.6 Intrusion events, where negative pressure creates back-siphonage of non-potable water into the distribution system, are not uncommon and can be caused by leaks, pipeline breaks, faulty connections, power outages, etc.7 Although unlikely, intentional contamination events in the distribution system are a concern where public water supplies are potentially vulnerable to bioterrorism threats.
The Iowa/WET study may show that healthy people consuming tap water from a well-run water utility exceeding federal standards isn’t associated with increased gastrointestinal illness, but how can you be sure that your utility is consistently well-run or exceeding federal regulatory standards? What about intrusion events, faulty distribution systems, or periodic treatment plant failures?
Regardless of what any study of a particular water source shows, one cannot deny that water is an ever-changing entity subject to a variety of natural and manmade influences. Foresight in predicting harmful changes in source water isn’t foolproof, evident by the fact that drinking water outbreaks continue to occur. Whether current research indicates that microbial waterborne infections are commonplace or rare from a particular source, there’s little debate that they can be costly, debilitating, result in long-term health effects or even death. Many waterborne outbreaks previously reported would have been prevented by the additional barrier that a POU water treatment device offers.
1. Harris, H.H., et al., “The chemical form of mercury in fish,” Science, Aug. 29, 2003: 1203, 2003.
2. Payment, P., et al., “A randomized trial to evaluate the risk of gastrointestinal disease due to consumption of drinking water meeting current microbiological standards,” American Journal of Public Health, 81:703-708, 1991.
3. Payment, P., et al., “A prospective epidemiological study of gastrointestinal health effects due to the consumption of drinking water,” International Journal of Environmental Health Research, 7: 5-31, 1997.
4. Craun, G., et al., “Outbreaks in drinking-water systems, 1991-1998,” Journal of Environmental Health, 65(1):16-23, 2002.
5. U.S. Centers for Disease Control and Prevention, “Morbidity and Mortality Weekly Report, CDC Surveillance summaries: Surveillance for waterborne disease outbreaks-United States, 1999-2000,” Nov. 22, 2002.
6. U.S. Environmental Protection Agency, Office of Water, Drinking Water Infrastructure Needs Survey, USEPA 816-F-01-001, February 2001.
7. LeChevallier, M., et al., “The potential for health risks from intrusion of contaminants into the distribution system from pressure transients,” Journal of Water and Health, 01:3-14, 2003.
8. NOW with Bill Moyers, “Science & Health: Food Fight--Mercury in Fish,” Public Broadcast System, July 18, 2003: www.pbs.org/now/science/mercuryinfish.html
9. Yang, S., “Home-treated Water No Better than Plain Tap in Preventing Gastrointestinal Illness, Finds New Study,” University of California-Berkeley, Sept. 25, 2003: www.berkeley.edu/news/media/releases/2003/09/25_water.shtml
About the author
Dr. Kelly A. Reynolds is a research scientist at the University of Arizona with a focus on development of rapid methods for detecting human pathogenic viruses in drinking water. She holds a master of science degree in public health (MSPH) from the University of South Florida and doctorate in microbiology from the University of Arizona. Reynolds has also been a member of the WC&P Technical Review Committee since 1997.