It all depends on the issues with your water. There are point of use systems which can treat the water at the sink which can be affective. The whole house systems are great if you have hard or soft water which needs treating to become palatable. i am very lucky to be in an area with great tasting water which requires no treatment. There are a lot of different types of systems so you need to know what you are trying to treat the water for to pick the right system. Check out this link for more info:
http://www.nsf.org/consumer/drinking..._treatment.asp