What is Reverse Osmosis?

Reverse Osmosis is the reversal of the natural flow of osmosis. In a water purification system, the goal is not to dilute a salt solution/contaminated water, but to separate the pure water from the salt and other contaminants. When the natural osmotic flow is reversed, water from the salt solution is forced through a membrane in the opposite direction by application of pressure, hence the term Reverse Osmosis.