Nuclear grade with color indicator. Color resin will change either from greenish to dark brownish color or from light brown to dark dark brown / off blackish color, when the resin is used up. This system is a RO+DI system it connects to the water supply, thence it produces water. Actually, the system flushes itself when And so it’s making water. All reverse osmosis systems, residential or commercial, are required to have drain waterwhen making pure water.