This four stage zero waste reverse osmosis system is one hundred percent efficient. The patented zero waste reverse osmosis system is the first ever that does not waste water. The reverse osmosis uses a semi permeable membrane, by applying pressure across the membrane, it concentrates contaminants like a strainer on one side and produces crystal clear water on the other side. This reverse osmosis systems produce both clean drinking water and waste water that is flushed from the system. Compared to all the other systems that can flush as much as 4 or more gallons for every 1 gallon of drinking water produced, the ZRO-4 is the world?s most efficient system. This system provides the high quality of water to any home at a fraction of the cost of bottled water. This system is tested and certified by NSF international against NSF and ANSI standard 58 for the reduction of the claims specified on the performance data sheet. IAPMO certified.