How Does Reverse Osmosis (RO) Work?


Reverse osmosis is one of the most critical water purification processes in use today. It plays an integral role in both municipal and industrial water treatment, removing a wide range of contaminants in a cost-effective way.

Modern technology has pushed it even further, improving recovery rates and making this process more accessible to communities in need of clean water.


Understanding this process first requires an understanding of osmosis. Osmosis is the process where water or other liquids pass through a semipermeable membrane. That semi-permeable membrane blocks certain dissolved materials from passing through but lets water pass through freely. 

When the concentration of dissolved materials is different on either side of a semi-permeable membrane, this difference in concentration is translated to osmotic pressure. Water will pass through to balance the concentration. Osmosis is found in many processes in nature and plays a key role in how cells work in any living creature.

Reverse osmosis reverses this process. Instead of using a difference in concentration to generate pressure, it uses pressure to create a difference in concentration. When pressure higher than osmotic pressure is applied, water moves back through the semipermeable membrane, leaving dissolved materials behind.

The end result is a small amount of water with a high concentration of dissolved materials and a larger amount of clean, purified water.


The utility of this Process in water treatment is clear. At the correct scale, reverse osmosis can quickly and efficiently remove contaminants from water. The semi-permeable membrane lets the water pass while the contaminants are blocked.

  1. The process begins with the feed water. This can come from a variety of sources, depending on the process. It could be groundwater that has contaminants that need removal, brackish water, seawater, wastewater being treated, or water that must meet strict standards for food and beverage manufacturing.

  2. A pump pressurizes the feed water and pushes it through the reverse osmosis unit. Inside, a semipermeable membrane prevents contaminants from passing through. The pressure from the pump forces clean water through the membrane, which goes on to further processing or final use.

  3. The unit also produces a highly concentrated reject stream containing some water and all of the captured contaminants. This waste is high in salt and other contaminants and must be disposed of accordingly.


ROTEC, a WFI Group business unit, implements this process in a variety of water treatment applications and models. Among the most notable applications is incredibly cost-effective and efficient desalination using our innovative Flow Reversal (FR-RO) technology for ultra-high recovery performance

ROTEC has developed a leading-edge  technology suitable for both new facilities and retrofits – upgrading existing plants. The improved recovery enables both municipal and industrial water treatment facilities to reduce costs when producing clean water.

Our unique flow reversal technology periodically changes the flow direction in the reverse osmosis process, switching the tail and lead elements. This inhibits both mineral scaling and biofouling, allowing the system to operate at higher recovery rates.


Reverse Osmosis (RO) is an established technology based on key physical properties of water and dissolved contaminants. It provides an efficient method to deal with many contaminants, and the latest Flow Reversal technology from ROTEC is making reverse osmosis even more economical, ecological and accessible via high recovery.
It can be an integral part of any municipal or industrial water treatment process., to achieve higher recovery rates in comparison with conventional RO technologies, while preventing scaling on the membranes and increasing water reuse. 



A: It is used in many water treatment applications to remove salts and contaminants. Both municipal, agricultural and industrial wastewater treatment benefit from this process. Other processes, such as seawater desalination, beverage production, and chemical industries, as well as the pharmaceutical, microelectronics, semiconductor and mining industries also use this technology.      

There are also environmental reasons for using the RO method when there is nothing else you can do with effluent.

A: The frequency of the flow reversal event is dependent on saturation and kinetics. This frequency which is specific for each water type/RO system is based on the induction time, ROTEC’s experts experience and knowledge, and preliminary experiments that are done in the beginning of the system operation – to dictate the system operation mode.