An RO system employs a semi-permeable membrane. The membrane is a thin, multi-layered sheet with pores so small that water molecules can pass through, but it acts as a barrier to dissolved solids like salts and other chemicals.
For example, place a membrane between two compartments in the container as shown. Then place a salt solution in one half of a container and pure water in the other. While the membrane will allow the water to pass through it, the salt cannot.

Ozone was first discovered in the Netherlands around 1900 and was subsequently used to purify drinking water as early as 1906. Ozone is now used to help purify water for municipalities, beverage manufacturing companies, bottled water manufacturers and fish farmers. Its usefulness is unlimited throughout business and residential applications.

Reaction with other materials (called oxidation) makes Ozone very attractive to help purify water.  Ozone attacks and destroys viruses, bacteria and other pollutants up to 3000 times faster than chlorine.  Ozone works so much more effectively and efficiently because it attacks the bacterial cell walls, creating instant cell destruction.

Unlike chlorine, Ozone is not a residual chemical in the reclaimed water.  In water, Ozone (O3) returns to oxygen (O2) in less than one hour. Ozone is fifteen (15) times stronger than chlorine.

Obviously, in a water purification system the goal is to remove the salt from the water. Fortunately the water can be forced to move in the reverse direction by applying pressure to the high concentration side. Pure water is then forced through the membrane leaving the salt behind. Thus the term "Reverse Osmosis".