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Hey, Culligan man – you’re fired!
Filtered water no better than top-quality tap in preventing gastrointestinal illness, new study finds

| 08 October 2003

A new study led by campus researchers 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 provides no additional protection from gastrointestinal illness.

In a year-long trial, researchers found no significant reduction in symptoms such as diarrhea, nausea, vomiting, or abdominal cramps in those who used a top-quality home water filter compared with those who used a placebo device.

“What our study suggests is that, if your tap water comes from a well-run municipal water utility, where the water [quality] exceeds government treatment guidelines, there does not seem to be a health benefit from using an in-home water-treatment device,” says John Colford, associate professor of epidemiology at the School of Public Health and principal investigator of the study. A 1994 EPA report showed that 30 million people, or 12 percent of America’s population, received drinking water that had violated one or more public health standards.

The Berkeley-led research team included scientists from the EPA and the U.S. Centers for Disease Control and Prevention; the two agencies 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. “For example,” says Colford, “in some 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 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” 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.”

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. Member utilities provide water whose quality exceeds federal guidelines. Several water utilities in the San Francisco Bay Area are 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. At the same time, he pointed out that the people in this study were healthy, so that investigators cannot say whether home water treatment systems would provide a benefit to people with health concerns, including those with compromised immune systems. He also acknow-ledged that filters could be used for reasons other than preventing gastrointestinal illnesses, such as taste or other non-health-related benefits.

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