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Drinking water supplied to more than a 100 million Americans contains toxic carcinogens, a new report by environmental health research organization the Environmental Working Group (EWG) claims.

The EWG is calling for new, lower limits of numerous chemicals in drinking water, especially for trihalomethanes (THMs), which are believed to cause the most harm. The group has also asked the U.S. Environmental Protection Agency (EPA) to carry out more research into almost 600 chemicals found in drinking water across the United States.

The report's findings reveal that over 200 of the biggest U.S. municipal water systems in 43 states contain THMs. The EPA defines trihalomethane concentration levels of under 80 parts per billion as safe, but EWG claims that this limit is too high and may have serious consequences for public health.

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International studies have found that much lower levels of THMs, or 35 parts per billion, could result in increased risk of several types of cancer, still births, miscarriages and birth defects, among others.

According to Jane Houlihan, EWG's senior vice president for research, millions of people drink tap water containing 20 to 30 contaminants on a daily basis. Moreover, the research found 119 chemicals regulated under the Safe Drinking Water Act in about 22 million drinking water samples. The effect of exposure to most of these chemicals is understudied or unknown, Houlihan added.