The right water filter can remove a range of contaminants: lead from old pipes in your home or the municipal water supply, chemicals such as atrazine and benzene, and chlorine from the treatment plant that gives your tap water a funny taste. Here’s how to identify what’s lurking in your water—and how to filter it out:

Check your supply. Water quality can vary depending on where you live. “It’s important to know where your drinking water supply comes from and if it contains any impurities that could pose a health risk,” says Mindy Costello, consumer information specialist at NSF International, a public-health standards and certification organization. If you pay a water bill, you should have access to an annual Consumer Confidence Report listing contaminants in your water. Go to the Environmental Protection Agency's page at epa.gov/ccr for more information.

Or have it tested. If you live in an old house that may still have lead pipes, or if you have a private well, you’ll need to get your water tested. Some state and local health departments offer free test kits. Check the EPA’s website for local testing labs or call its Safe Drinking Water Hotline at 800-426-4791.

“Some typical testing results may include coliform bacteria, E. coli, nitrate/nitrite, arsenic, hardness, volatile organic chemicals, metals, lead/copper, and inorganic chemicals,” Costello says. Fees range from about $50 for a single lead test to several hundred dollars to test for multiple contaminants.

Choose a filter. If your results raise concerns about contaminants in your drinking water, a point-of-use filter is the best remedy. Options range from simple carafe-style filters that you fill by hand (the Clear2O CWS100, $30, is CR’s top-rated model) to undersink systems that often require professional installation (we recommend the Multipure MP750SB, $430). To be assured that a filter will remove a certain contaminant, the package should specify that the filter meets NSF certification for that substance.

Another option is a whole-house filter, also known as a point-of-entry filter. These systems are generally designed to remove sediment, rust, and sometimes chlorine, though not harmful contaminants such as lead.