It's important to know what, if any, contaminants are in your water before you buy a filter. Then you can match the filter to the problem. Also consider how much water you consume vs. how much effort and disruption to your daily routine you're willing to tolerate.
Water filters can improve the taste of your water, and they may even protect you from harmful contaminants. Our tests of carafe filters and faucet-mounted, undersink, countertop, and reverse-osmosis models found options suitable for removing lead and many common contaminants.