Reverse Osmosis involves:
• The application of pressure greater than osmotic pressure of solution.
• Diffusion of water but not salt through a semi-permeable membrane in direction opposite of natural flow.
• Crossflow filtration to sweep away concentrated salts.

Reverse Osmosis can:
• Remove purified water from a feed stream (permeate)
• Concentrate chemicals in a feed stream (reject)
• Selectively separate small ions and molecules

Reverse Osmosis cannot:
• Concentrate to 100%
• Separate to 100%
• Distillation can sometimes be a more cost effective solution

At the heart of the Reverse Osmosis system is the RO membrane. The semi-permeable nature of this membrane allows the water to pass much more readily than the dissolved minerals. Since the water in the less concentrated solution seeks to dilute the more concentrated solution, the water passage through the membrane generates a noticeable head difference between the two solutions.This head difference is a measure of the concentration difference of the two solutions and is referred to as the ‘osmotic pressure difference’. When a pressure is applied to the concentrated solution, which is greater than the osmotic pressure difference, the direction of water passage through the membrane is reversed and the process that we refer to as Reverse Osmosis is established.