Typically, the water goes through a post-filter on its way to the faucet. A shut-off valve is an integral part of the system that helps reduce the amount of water directed to waste. RO systems produce excellent drinking water, but quality comes at a cost. A typical under-counter RO system will send 8 gallons of water to waste for every gallon of treated water. This wasted water can be minimized by the shut-off valve that sends water to waste only while the RO system is actually producing treated water.
Percent recover y measures the highest efficiency that the RO system can achieve.
This measurement is taken with no backpressure on the membrane and is not the best indicator of the system's efficiency. Percent efficiency is calculated for RO systems with storage tanks and shut-off valves. Percent efficiency, a more realistic indicator, expresses the amount of clean water produced as a fraction of the total water used. Reverse osmosis systems are sensitive to the quality of the untreated water. Particulates, iron, and very hard water can foul the membrane and reduce water production rate and quality.