According to the EWG report, you should be very afraid of what could be coming out of your home's taps. A host of hormone-disrupting chemicals can contaminate water sources – and they're much more common than you'd think, says Sharp. For instance atrazine, a pesticide used on most corn crops in the U.S., leeches into the earth and waterways and, consequently, can taint the water supply. "Atrazine has been linked to delayed puberty and prostate inflammation in animals," Sharp says. "Some studies have even tied it to prostate cancer in humans."

Another chemical quickly becoming a big problem is perchlorate, a component found in a variety of places: rocket fuel, fireworks, batteries, car parts, and some old fertilizers. Sharp says it directly messes with the thyroid by hindering the gland's uptake of iodine, an essential mineral. According to the California Department of Toxic Substances Control, this contaminant has already been found in groundwater or soil in 20 states. And currently there is no federal drinking water standard for perchlorate, Sharp notes.

Lead is still an issue for many of us. "Usually it won't be in the water itself, but old fixtures and pipes can contain lead," says Sharp. "Even if clean water starts out clean, it flows through pipes and fixtures and becomes contaminated. Many people think this type of lead exposure is a problem of the past, but unfortunately it's still all too common."

Determining which, if any, of these toxins might be present in your tap water can be tricky. For starters, check with your local water utility company, which may be able to tell you which chemicals could be present, but Sharp suggests staying safe and installing a water filter. There are several types, including reverse-osmosis, deionizing, and carbon block, which work better for different systems and contaminants. Consult the EWG's Water Filter Buying Guide to find an appropriate model.