Osmosis is the phenomenon of water flow through a semi-permeable membrane that blocks the transport of salts or other solutes through it. Osmosis is a fundamental effect in all-biological systems. Osmosis is applied to water purification and other chemical laboratory and industrial processes. When two water volumes are separated by a semi-permeable membrane, water will flow from the side of low solute concentration to the side of high solute concentration. The flow may be stopped or even reversed by applying external pressure on the side of higher concentration. This is called reverse osmosis. (R.O.) Reverse osmosis is only one stage of a typical R.O. system. Sediment and carbon filtration is normally included with an R.O. system, with each stage of filtration contributing to the purification process.

1. The first stage of filtration is the sediment filter, which reduces suspended particles such as dirt, dust, and rust.
2. The second stage of filtration is the carbon filter, or filters which reduce volatile organic chemicals, chlorine, and other taste and odor causing compounds.
3. The heart of Reverse Osmosis is the membrane. It is responsible for rejecting up to 98% of the total dissolved solids in the water. This is where the purification takes place.