Product review (5 stars): Simple installation - when you do it right
The water filter installs bayonet-style with an easy, quarter-turn twist.  The mounting device that the filter attaches to has what appears to be a built-in valve piece which also turns a quarter-turn when installing the filter.  Make sure when inserting the new filter that the inlet and outlet nipples on the filter properly insert all the way up into the two, round holes in the valve device (the mounting device) before turning the filter, otherwise the built-in valve may get turned part way thus preventing proper installation.  When everything is lined up properly the new filter goes in with minimal effort.  If you encounter significant resistance when making the quarter-turn, stop and check the valve piece and make sure that it is turned fully counter-clockwise (as you are looking at the two holes that the nipples go in to).  Then insert the filter again and turn.  It really is very simple when you do it right (which I didn't do the first time)!  This is my second RC-EZ-4 (the replacement filter #).  I believe it does an awesome job filtering my lousy tasting tap water and makes our drinking water from the fridge taste great!  I love it!