First, when selecting a countertop water filter, you will want to make sure that the filter is simple to install.  The kit should be designed for the non-mechanically inclined, and include all the tools and instructions you’ll need to get it up and running in half an hour to an hour.  Second, look at the specs of the filter.  You’ll want to make sure the filter is high-grade and designed to eliminate biological matter as well as harmful chemicals and heavy metals.  Finally, look for special features that you and your family will enjoy.  Some countertop filters will pump out hot or cold water, add flavor to the water, or even heat water to the correct temperature to prepare soup or tea.