What are the variations of osmosis?

The two variations of osmosis are reverse and forward osmosis. Reverse osmosis is a water purification process that uses a semi-permeable membrane to remove ions, molecules, and larger particles from water. It works by applying pressure to the water on one side of the membrane, forcing it through the membrane while leaving behind contaminants. The membrane used in reverse osmosis is designed to allow only water molecules to pass through while blocking larger particles and solutes (up to 99.99%). Thus, it results in purified drinking water. 

Forward osmosis is a process that utilizes the natural osmotic gradient between two solutions to achieve water purification or concentration. Unlike reverse osmosis which requires external pressure, forward osmosis relies on the osmotic pressure difference between a dilute solution (the feed solution) and a concentrated solution (the draw solution) separated by a semi-permeable membrane. Water naturally moves from the diluted solution to the concentrated solution, driven by the osmotic pressure gradient.