At odds with other research, a new study is suggesting that drinking tap water poses only a slight risk of having a miscarriage, if at all.¹ The study was sponsored by the American Water Works Association (AWWA) Research Foundation and the Environmental Protection Agency (EPA).

"Our study does not completely negate the evidence from toxicology studies or other epidemiologic studies, but does make it less worrisome than it was before," explained David Savitz, PhD, chairman of the department of Epidemiology at the University of North Carolina at Chapel Hill, who led the research, in an interview with Priority Healthcare.

However, the findings run counter to those of a study published seven years ago² that reported an increased risk of miscarriage linked with consuming high amounts of cold tap water containing high levels of certain chemicals.

A Chemical Interaction
"Chlorine is commonly used to accomplish disinfection [in potable water]," wrote Savitz and his colleagues in their study paper, published online at the website of the AWWA Research Foundation. "However, the interaction between chlorine and organic material in drinking water sources produces a wide range of chemical disinfection by-products, which may pose health risks."

The organic material consists of natural vegetation found in lakes, rivers, or other types of surface water, said Savitz, which is mostly, but not completely, removed prior to chlorination.

Comparing Chemical Levels to Water Use
To assess the risk of pregnancy loss posed by these chemicals in tap water, the research team recruited more than 3,000 women who were either planning a pregnancy or were in early pregnancy. The study participants underwent ultrasound exams and completed two telephone interviews that collected information on their water use. This included not only consumption, but bathing or showering habits, since the chemicals can potentially be absorbed through the skin. About half of chlorine by-products in the body originate from skin contact or inhalation, Savitz explained.

The investigators also measured levels of disinfection by-products regularly at three water treatment plants that serve the area in which the study participants live. Included in those measurements were the chemical concentration in tap water, amount consumed, bathing and showering exposure, and integrated exposure.

Among the chemicals tested are known as trihalomethanes (try-hay-loh-METH-anes). These substances have been found to cause cancer in animal studies.^3,4

The study lasted a total of six years.

Weak Link Uncovered
Eventually, while Savitz and his fellow researchers found a risk of pregnancy loss related to the drinking water chemicals bromodichloromethane and dibromochloromethane—two types of trihalomethanes—the risk was much weaker than in previous research. As a result, even drinking large amounts of water containing trihalomethanes does not increase the risk of miscarriage, the study authors wrote. "Several specific drinking water disinfection by-products were evaluated for a relationship to pregnancy loss and, in general, no strong associations were found," they wrote.

Still, they stress that because they found "sporadic" evidence of an increased risk of miscarriage and fetal growth restriction, however minute, more study is necessary to confirm the findings.

The Flip Side
In the opposing study cited, published in 1998 by a team of researchers in the California Department of Health Services,² exposure to trihalomethanes was examined in relation to its influence on miscarriage risk. The prospective study involved more than 5,000 pregnant women enrolled in a prepaid health plan.

The researchers collected trihalomethane sampling information from nearly 80 drinking water utilities in the area, and then compared that information with each woman's consumption information.

The researchers determined that exposure to trihalomethanes doubled a woman's risk of having a miscarriage. This was especially true for bromodichloromethane, they wrote. This chemical "was associated with [miscarriage] both alone and after adjustment for the other trihalomethanes," they concluded.

But Savitz says the methods used in his study were more solid, adding that he cannot explain how the researchers in the earlier analysis reached their conclusions, given the fact that most flawed studies lead to false-negative results, not false-positive ones.

Researcher: Concern is Unwarranted
In the meantime, he advises women that it's safe to drink tap water without worrying about increasing their risk of miscarriage. "In my opinion, the evidence overall, not just from our study, would at most justify a very low level of concern or interest, such that ignoring the issue completely and drinking tap water as desired is a perfectly reasonable option," Savitz said, adding that the risks associated with tobacco or caffeine consumption are "far stronger".

Still, for women who are concerned, Savitz recommends using tap or pitcher filters, though he says it's difficult to avoid exposure to the chemicals in showering or bathing.

1. Savitz DA, Singer PC, Hartmann KE et al. Drinking Water Disinfection By-Products and Pregnancy Outcome. Available at: http://www.awwarf.org/research/TopicsandProjects/
execSum/PDFReports/91088F.pdf. Accessed August 24, 2005.
2. Waller K, Swan SH, DeLorenze G, Hopkins B. Trihalomethanes in drinking water and spontaneous abortion. Epidemiology 1998 Mar;9(2):134-40.
3. DeAngelo AB, Geter DR, Rosenberg DW, Crary CK, George MH. The induction of aberrant crypt foci (ACF) in the colons of rats by trihalomethanes administered in the drinking water. Cancer Lett 2002 Dec 10;187(1-2):25-31.
4. Geter DR, George MH, Moore TM, Kilburn SR, Huggins-Clark G, DeAngelo AB. The effects of a high animal fat diet on the induction of aberrant crypt foci in the colons of male F344/N rats exposed to trihalomethanes in the drinking water. Toxicol Lett 2004 Mar 7;147(3):245-52.

John Martin is a long-time health journalist and an editor for Priority Healthcare. His credits include overseeing health news coverage for the website of Fox Television's The Health Network, and articles for the New York Post and other consumer and trade publications.