Faucet filters are miniature versions of the big carbon filters a lot of cities are now using to scrub municipal water clean. They come in various sizes and contain different types of replaceable filters geared to strain out specific impurities in your tap water. One baseball-size version screws onto the end of your kitchen faucet. Another, about the size of a small loaf of bread, taps into your cold-water line under the sink.
Different brands vary substantially in the kind and amount of substances they filter out.
To avoid the unnecessary expense of buying a product that does far more than you need, make sure the filter you choose is NSF-certified as capable of removing the specific contaminants found in your water. Those can be anything from rust and chlorine to such serious health threats as Cryptosporidium, trihalomethanes, and lead. The main advantages are convenience and cost. Because these simple devices attach directly to your plumbing, you get hundreds of gallons of clean water before you have to replace a filter. And because carbon filters vary widely in cost and effectiveness, you can choose to go low-budget if you need to remove only one or two substances.