CleanTapTM filter monitor is an electronic device which measures the amount of water passing through the filters. A light indicator, green, yellow and red is installed on the clean water faucet. An electronic sensor module is connected to the tubing under the sink and measures the flow to the faucet. When the filter is good, the green light flashes when the faucet is on. When the filter has been used 80%, the yellow light flashes, and at 100%, it goes red. The CleanTap can be set at 500, 1000, or 3000 gallons. The CleanTap is also available as a kit to add to existing units. Battery operated.