Basically you use the waste water from the first membrane housing and feed into the second membrane housing which works if you have sufficient water pressure to the unit

During this operation the second or third cartridge insures that the water leaving the system is of the highest purity

Always from reputable manufacturers

Color changing resin changes color from blue to amber as resin is used up (exhausted)

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Triple Filter Bracket (Steel) NSF Certified Basically you use the wasteTriple Filter Bracket (Steel) This is a powered coated steel triple filter bracket. It can accommodate up to three standard 10 " filter housings. It is white in color and very sturdy. Dimensions and Weight Dimensions: Width: 14. 0" X Height: 2. 0" X Depth: 5. 75" Weight : 2. 0 Pounds