How Reverse Osmosis water filters work

For nearly every creature on the planet, water is an important part of life. For humans, clean and pure water is most obviously crucial for drinking, cooking and cleaning purposes. Without clean water, it is impossible to maintain good health or a clean and healthy lifestyle. In some areas, limited water supply may cause people to look to sources of water that are not ideal for consumption, such as seawater. To ensure that water is clean and safe to drink, a process known as reverse osmosis may be used to remove harmful impurities and minerals. For residential and commercial use, there are reverse osmosis filters that can be attached to a sink for the purpose of purification.

What is Reverse Osmosis?

Reverse osmosis is a purification process that removes nearly any type of contaminant, or impurity, from solutions. This includes bacteria and pathogens that can cause diseases, as well as salt from saline solutions. It involves the use of a semipermeable membrane and pressure to filter clean water from impure solutions. This process is frequently used to purify water for the purpose of drinking. The process itself is the reverse of the process known as osmosis.

Process of Reverse Osmosis

Reverse osmosis is achieved by using a tank of water that is bisected by a fine membrane that serves as a filter. The pressure from the incoming water pushes it through the membrane. The reverse osmosis membrane contains small holes that will not allow anything larger than .001 microns to pass through. As a result, clean water moves through the membrane and any impurities such as sodium, arsenic, mercury or lead are held back, or filtered out.


Desalination is a process that makes seawater drinkable by removing all of the salt and impurities. Desalination using reverse osmosis filters is a common technique in use around the world. The difference between this and regular reverse osmosis is that pretreated seawater or other brackish water enters the filter as opposed to tap water. Pretreatment adjusts the pH levels of the water and inhibits scaling. The pump then pressurizes the pretreated water to begin the separation process in which fresh water is pushed through the membrane and the dissolved salts are rejected.

Reverse Osmosis Filter Components

Reverse osmosis filters consist of several parts that are crucial to their successful operation. The filters have their own faucet that is attached to the sink, and a storage tank that holds the purified water until it is ready for use. The membrane is the most often discussed feature of the filter. This is because it removes the impurities and, as a result, is the most important part of the system. From this membrane there runs a drain line through which the impurities leave the system.

Before the membrane however, there is a pre-filter that removes chlorine or sediment, such as sand and silt. After the pure water leaves the storage tank of the reverse osmosis filter, it goes through what is called a post filter. This filter removes odors and anything that may cause a bad taste from the water before it comes out of the faucet. There are several valves on the filter, including an automatic shut off valve that stops water from passing through the membrane when the storage tank is full. A check valve prevents water from flowing back out of the storage tank.


The effectiveness of reverse osmosis filters is extremely high, although they typically do not remove 100 percent of elements. The amount of particles and impurities removed typically ranges between 80 and 98 percent. The actual amount that is removed depends on the amount of pressure and the quality of the membrane. To ensure the continued effectiveness of the reverse osmosis filter, both the pre- and post-filters should be checked and replaced periodically. In addition, the integrity of the membrane must also be evaluated for maximum performance.


As reverse osmosis is the purification of water it has a number of applications for consumers and professionals, such as those in the medical industry. Reverse osmosis filter systems are commonly used in homes and are attached to the bottom of a sink to purify the water for cooking, drinking and other residential uses. For medical purposes, reverse osmosis filters are used for creating the processed water needed for dialysis treatments. Pharmaceutical companies also use reverse osmosis to process grade water that is used in some pharmaceutical applications. Other examples of applications that use reverse osmosis include the desalination of seawater to create pure drinkable water, the creation of pure water for the semiconductor industry, and the treatment of waste water.