Assuming that you already understand what reverse means, let’s remind ourselves what osmosis is. Osmosis refers to the natural movement of molecules of a solvent from a less concentrated solution to a solution that has a higher concentration through a semipermeable membrane. In reverse osmosis, it’s the opposite that happens. Water molecules move from a solution of water contaminants leaving you with pure drinkable water on one side and most of the contaminants on the other side. Since reverse osmosis goes against the principles of osmosis, energy in form of pressure has to be applied to make it a success. That’s why reverse osmosis filtration systems utilize a pump that pushes the contaminated water through a special semi-permeable reverse osmosis membrane.