One of the common pharmaceutical products found in tap water is estrogen, much of which is inadvertently released into sewers through the urine of women taking birth control. Studies have shown that estrogen can wreak reproductive havoc on some fish, which spawn infertile offspring sporting a mixture of male and female parts. Researchers at the University of Pittsburgh found that human breast cancer cells grew twice as fast when exposed to estrogen taken from catfish caught near untreated sewage overflows. “There is the potential for an increased risk for those people who are prone to estrogenic cancer,” said Conrad Volz, lead researcher on the study. What may be more troubling is the mixture of contaminants and how they might interact to cause health problems. “The biggest concern is the stew effect,” says Scott Dye of the Sierra Club’s Water Sentinels program. “Trace amounts of this mixed with trace amounts of that can equal what? We don’t know.” Estrogen can affect aquatic life even in extremely small amounts. In 2008, a researcher for Johnson & Johnson calculated that toxic effects on fish from estrogenic substances could be expected at concentrations as low as 350 parts per quadrillion. “If you can imagine 350 parts per quadrillion,” Snyder says, “it’s unimaginably small, but yet it can have a measurable impact on fish.” With such contaminants proving elusive to municipal filtration systems, the burden of protection often lies with the end user. But getting traces of birth control and other drugs out of your tap water isn’t so easy. Of the many different kinds of in-home water filtration systems available today, only those employing reverse osmosis have been shown to filter out some drugs. Some makers of activated carbon water filters claim their products catch pharmaceuticals, but there has been little independent research to verify carbon’s effectiveness with the many drugs that have been found in water supplies. “The best choice,” says Cathy Sherman of the natural health website Natural News, “would probably be a combination of a reverse osmosis filter augmented by pre- and post-activated carbon filters.” Installing such a system just for drinking water is sufficient, she says, given that water used for cleaning and plumbing doesn’t typically get ingested. It should be noted that virtually all undersink reverse osmosis units contain at least two stages of carbon as well as the reverse osmosis membrane. As to prevention, NSF International, urges individuals to not use their toilets or sinks to dispose of unused medications and to opt for the garbage instead; most modern landfills are lined to keep such contaminants inside. Reference: Scientific American.Estrogen in Tap Water: How to Remove It.