THE REVERSE OSMOSIS MEMBRANE
Cross Section of a Typical Membrane

How the R.O. Membrane Works:

When the reverse osmosis system is operating, feed water flows into one end of the membrane housing element as shown above. It flows across the wound membrane. Because there is pressure on the water, reverse osmosis takes place. Water flows through the membrane to the core, while the dissolved minerals remain on the feed side. The water that flows through the membrane is called "permeate". The permeate, or product water from the membrane, is now safe to drink. The rate of production is relatively slow. Normally a storage tank is used hold the finished water until it is needed. When the tank is full, the system will automatically stop making R.O. water.

Not all of the water flows through the membrane. Only 25-50% of the water becomes permeate. The remainder stays on the feed side of the membrane and flushes away the dissolved minerals. this water is called the "concentrate". The concentrate plays an important role in the operation of the membrane. As the permeate flows through the membrane, the concentrate retains almost all of the minerals that were in the original feed water. The TDS (total dissolved solids) of the concentrate rises. As it flows past the membrane, it carries away the minerals, in effect washing the surface of the membrane. It is eventually piped out to the drain. If the concentrate did not carry away the minerals, the membrane would foul or plug-up, acting like a filter which fills with particles and must be changed. Proper concentrate flow across the membrane will generally mean many years of high quality water from the membrane.

Comparison of the sizes of materials rejected by reverse osmosis membrane.

APPROXIMATE REJECTION RATES OF VARIOUS IMPURITIES: