The water barrier keeps the water from getting between the inner metal door framing and the removable door panel itself. Here is what it should look like....and it should be installed.... If not there, there is a possibility that water running down the window could run down the door panel and drain into the interior of the car. Not good.... I would want them in place.....and even use them on all the cars I have restored and own, including my beater '93 Bronco.