I have the Outerwear's pre-filter on mine, and never gave it much thought when I wash it... Last weekend, we drove through a torrential downpour on the way to the Scheid Diesel Extravaganza(the area we drove through got 5"-6" of rain) and the filter is fine. . I do have a heat shield which I'm sure helps to protect it, but after driving through the above mentioned rainstorm with no problems, I'm not going to worry about it anymore.