In its simplest presentation reverse Osmosis and ultra filtration system is a membrane process. That acts a molecular filters to remove (Permeable to water not salt and separating pure water and salt solution, by applying external pressure) dissolved mineral, organic, inorganic and heavy metals. It will also remove microbial matter including bacterial spores and viruses, which cannot remove by any ion exchange technique from water and wastewater.

Reverse osmosis has emerged as a serious alternative to chemical treatment systems due to a number of reasons. The minimal use of chemicals makes it environmentally desirable. Reverse osmosis is a simple process and the operational and maintenance costs are lower. It has higher production capacity to space ratio via-a-via other technologies. Ion exchange processes, on other hand, incur high resin replacement costs, substantially higher regeneration costs and inordinate downtime costs due the need for replacing ion exchange columns. While the biggest operating costs for ion exchange systems are regeneration chemicals, the major cost component in RO is energy i.e. electrical power to operate the RO feed pump.