Home-treated water no better than plain tap in preventing gastrointestinal illness, finds new study
BERKELEY – A new study led by researchers at the University of California, Berkeley, should make some people feel better about the next cool glass of tap water they get at home. The study found that, in homes served by well-run water districts, an in-home water treatment device provided no additional protection from gastrointestinal illness.
In the year-long randomized and blinded intervention trial, researchers found no significant reduction in symptoms such as diarrhea, nausea, vomiting or abdominal cramps in those who used the home-filtered water compared with those who used a placebo device. The UC Berkeley-led research team included scientists from the U.S Environmental Protection Agency (EPA) and the U.S. Centers for Disease Control and Prevention (CDC).
The study will be reported at a meeting of the International Society of Environmental Epidemiology in Perth, Australia. The results will be presented Friday, Sept. 26 in Australia, or Thursday, Sept. 25 in the United States.
"What our study suggests is that if your tap water comes from a well-run municipal water utility, where the water exceeds government treatment guidelines, there does not seem to be a health benefit from using an in-home water treatment device," said John Colford, associate professor of epidemiology at UC Berkeley's School of Public Health and principal investigator of the study.
The EPA and the CDC funded the water evaluation trial, also known as the WET study. Its goal was to test whether additional in-home treatment of drinking water that meets federal and state treatment guidelines could effectively reduce the incidence of gastrointestinal illnesses. The results of previous studies on the issue have been mixed.
"Some of the prior trials had different designs which may have led to biased results," said Colford. "For example, in some of the earlier studies, participants knew whether or not they were using an active treatment device in their homes. Our study was designed to minimize this and other forms of potential bias as much as possible."
More than 1,200 healthy adults and children from 456 households in Iowa took part in the trial. They were all customers of the Iowa-American Water Company, which treats water from the Mississippi River.
Participants were randomly assigned to one of two groups. One group used a top-of-the-line treatment device that combined a 1-micron filter with an ultraviolet light chamber designed to remove or neutralize any microbes in the water. The other group used a so-called "sham device" that looked identical to the active filter, but that did not treat or change the taste of their regular tap water. The devices were connected to the kitchen faucet where people obtained the majority of their drinking water. Participants were also instructed to fill water bottles from the devices to carry to work or outside the home when possible.
After the first six months of the study, those who started off using the active treatment device were switched to the sham device for the remainder of the trial. Those who used the sham device switched to the active device. Neither the participants nor the researchers knew which device they were using during either phase of the study.
During the first six months, there were 707 episodes of illness reported by those with the active device, and 672 episodes reported by those with the sham device. During the second half of the study, participants reported 516 and 476 episodes of illness in the active and sham device groups, respectively. The differences between the groups were not statistically significant.
"It didn't matter whether people used or didn't use an active water treatment device," said Colford. "We saw no significant difference between the groups with respect to symptoms that would suggest infectious diseases that may be caused by microbes in the water."
Co-author Tim Wade, who was the project director for the study while he was a PhD student in epidemiology at UC Berkeley, noted that the study was limited to gastrointestinal illnesses and not to longer-term health effects that may be linked to chemicals such as lead and chlorine by-products.
"We only conducted the test in one water treatment system, which is recognized as one of the best in the country, so we would need to do further tests before we generalize these results to other utilities," added Wade, who is now a post-doctoral researcher at the EPA.
He pointed out that Iowa-American is a member of the Partnership for Safe Water, a voluntary cooperative effort between the EPA and water utility systems to improve water quality in the United States. An estimated 2 percent of the country's water utilities that use surface water as their source are enrolled in the partnership, whose members exceed federal guidelines for drinking water.
The partnership was formed in response to a 1994 EPA report showing that 30 million people, or 12 percent of America's population, received drinking water that had violated one or more public health standards.
Several water utilities in the San Francisco Bay Area are also members of the partnership, including the San Francisco Public Utilities Commission, the East Bay Municipal Utility District and the Contra Costa Water District.
Colford said the study's results are encouraging for other utilities that exceed federal guidelines for safe drinking water. "Water that comes from exemplary utilities may also provide adequate protection against gastrointestinal illnesses for a healthy population," said Colford.
He pointed out that the people in this study were healthy, so they cannot say whether home water treatment systems would provide a benefit to people with health concerns, including those with compromised immune systems.
He acknowledged that filters could be used for reasons other than preventing gastrointestinal illnesses. "Home water filters are often marketed for taste or other benefits," said Colford. "This study, however, did not evaluate taste or other potential benefits."
The study was funded by the EPA through an interagency agreement to meet requirements of the 1996 amendment to the Safe Drinking Water Act. It will be used along with other studies in a future EPA report on the National Estimate of Waterborne Disease.