Assume a membrane is semipermeable, allowing water to pass through while being closed to dissolved salts. Place a membrane between two compartments in a container. Then place a salt solution in one half of the container and pure water in the other half. Now a law of attraction happens. That is, two different concentrations of liquids within the same system will try to reach equilibrium (i.e. the same concentration of contaminants) on both sides of the membrane. Of course the only way for this to happen is for pure water to pass through the membrane to the salt water side in an attempt to reach equilibrium is called OSMOSIS.
Posted in: P-RO Reverse Osmosis System