One way to find out is to check your consumer confidence report, or CCR. The EPA requires utilities to provide a CCR to their customers every year. You may also find the CCR printed in your newspaper or posted on your local government website.
Our recent analysis of CCRs from the 13 largest U.S. cities revealed that few claimed to have no federal water-quality violations. Though none of the other water systems were consistently unhealthful, all had some samples containing significant quantities of contaminants. In New York City, for example, some samples had lead levels several times the federal limit.
Note that a CCR might indicate safe levels of a contaminant when your water actually has experienced potentially harmful spikes. Also, a CCR tells you about the water in your municipality, but not necessarily about what's coming out of your particular tap. Only testing your home supply can do that. Homeowners with a well on their property face even greater uncertainty, because such water isn't surveyed or reported on in CCRs. Call the EPA's Safe Drinking Water Hotline (800-426-4791) for the names of state-certified testing labs or for your local health authority, which might offer low-cost or free test kits, or check out www.epa.gov/safewater/labs. Ultimately, you might find that you don't need a water filter.
It's important to know what contaminants are in your water that so you can match the filter to the problem. Claims about contaminant removal vary from product to product, so read the fine print. Also, consider how much water you consume vs. how much effort and disruption to your daily routine you're willing to tolerate. Generally, the more contaminants you need to remove, the more complicated the filter, though there are trade-offs.