Reverse osmosis is a specific technology that can be used to eliminate a large majority of purifications and contaminants from water. It does this by using pressure to push the water through a semi-permeable membrane. To truly understand the process and purpose of reverse osmosis, it is first important to understand osmosis as a naturally occurring process.
The naturally occurring phenomenon called osmosis is perhaps the most important process that we find in nature. It is a simple process that allows a weaker saline solution to migrate towards a stronger saline solution. One of the best examples of osmosis is when the root systems of a plant draw water from the soil. Simply put, any solution that has a lower concentration will have a natural tendency to travel to a solution that is of a higher concentration.
For example, what would happen if you put 2 containers of water side by side? One of the containers of water would have a low salt concentration and the other container would have a high salt concentration. The 2 containers would need to be separated by a semi-permeable membrane. You would notice that the container of water with a low salt concentration would automatically begin to travel towards the container with a high salt concentration. Remember, however, you would need to have a semi-permeable membrane for this to work.
A semi-permeable membrane is simply a type of membrane that permits certain molecules or atoms to pass through whereas other atoms or molecules cannot. A good example of this would be a screen door that permits fresh air to enter into a home but does not allow pests or insects that are larger than the holes in the screen door to pass through. Another good example could be a type of Gore-tex clothing fabric. The fabric has holes that will allow water vapor to pass through but these holes are small enough so that liquid water does not pass through.
Reverse osmosis is simply the natural process of osmosis in reverse. Osmosis occurs naturally without any additional energy but to reverse this process you will require an energy source. The semi-permeable membrane that is used for reverse osmosis allows all of the water molecules to easily pass through but it prevents any organics, pyrogens, bacteria, or dissolved salts from passing through. However, a reverse osmosis system will need to have pressure applied to the water so that it can pass through the semi-permeable membrane.
Reverse osmosis can remove up to 99%+ of particles, dissolved salts, organics, pyrogens, colloids, and bacteria from a feedwater source. However, this type of system cannot remove 100% of viruses and bacteria. A reverse osmosis semi-permeable membrane will reject all contaminants based on their charge and size. It is a very effective system for treating surface, brackish, and groundwater for both small and large flow applications. Various industries use this type of system including boiler feed water operations, pharmaceutical companies, metal finishing plants, beverage and food processors, and semiconductor manufacturing, just to name a few.