A little FYI on the subject. Since there seems to be a conflict between it being called a water in fuel sensor or a fuel filter restriction sensor, I may be able to shed some light on it in case anyone is not aware of the following. Most diesel fuel filters are designed to swell up if they get wet with water so they do no allow fuel to pass through them. With that said, I can see where it is called both. If I had to guess, I would be willing to bet, it senses the pressure on the output side of the filter and only knows if there is not enough fuel being allowed to come through the filter. In other words, it works in either case; If water has it swelled up enough not allowing fuel to pass through it or trash has restricted fuel from passing through it.
Any way, thanks for everyones replies! I have it plugged off for the time being, but will order one from NAPA this week.