In a water flow application, the reed switch is secured to a stationary object while the magnet is placed on the moving paddle or baffle. The water flow will cause the paddle to rotate with the magnet actuating the reed switch. As the water filter collects debris, this will cause reduced water flow, slowing the paddle speed and thereby producing fewer switching operations. The reed sensor detects the paddle speed and sends signals to a processor which will illuminate the appropriate filter status light.