The Basics of Reverse Osmosis

Reverse osmosis produces bottled water quality hydration in your home. Nutritionists recommend drinking half your body weight in ounces daily.


An RO system removes harmful contaminants, including bacteria (like cryptosporidium and giardia), as well as metals and salts. It also polishes drinking water with a postfilter. A storage tank holds RO water so you have it on hand when you need it.

Water Pressure

Reverse Osmosis is a sophisticated technology that requires adequate water pressure to operate. Low water pressure will restrict flow and reduce the rejection rate, resulting in poor quality water. The water temperature also plays an important role in the overall performance of the system.

Reversing osmosis works by separating a concentrated aqueous solution from a freshwater solution with a semipermeable membrane. When pressure is applied to the side of the membrane with a higher concentration of solute, solvent molecules are forced through the membrane into the lower-concentration area. This movement of pure solvent is driven by osmotic pressure, which diminishes as the concentration gradient between the two sides of the membrane decreases.

To maintain proper water pressure, a reverse osmosis tank should be pressurized regularly. This can be done by shutting off the system and using an air pump to increase the tank pressure to around 7 PSI. This can be done with a bicycle pump or even an air compressor as long as you are careful to avoid over-pressurizing.

Another way to improve the water pressure of your reverse osmosis system is to move the tank closer to your faucet. This will make it easier to push the water through the last filter and into your home’s plumbing. Having larger tubing will also help to improve the system’s overall flow and performance.

Membrane Size

The pore size of the membrane is one of the most important factors when choosing an RO system. The pore size determines how much of the contaminants, salts and other molecules can make it through the filter. The smaller the pore size, the less water can pass through. This means that the system is more effective at rejecting contaminants.

There are four commonly accepted types of membrane filtration based on the pore size: reverse osmosis, nanofiltration, ultrafiltration and microfiltration. Each type uses a different method to separate substances.

Reverse osmosis is a type of membrane separation that produces clean water by forcing liquid through a semipermeable membrane under high pressure. It removes a wide variety of contaminants and sediment from drinking water, leaving only pure H2O behind. This process is great for industrial applications, including food and beverage processing, metal finishing and semiconductor manufacturing.

A reverse osmosis system is capable of removing 99%+ of dissolved salts (ions), particles, colloids and organics from water. It can also remove bacteria, fungus and viruses. These systems should be used in conjunction with UV disinfection to ensure that any living organisms are completely removed. Bacteria can grow on the RO membranes and be carried into the drinking water supply if they aren’t treated with proper disinfection techniques. This is why the use of pre- and post-filters is necessary to prevent fouling of the membrane.

Membrane Material

A membrane is a semi-permeable thin layer of material that separates contaminants according to their physical/chemical characteristics. The membrane is forced to move solvent molecules from the side where the solute concentration is high to the side where the solute concentration is low by applying pressure greater than osmotic pressure (the water potential difference).

Reverse osmosis removes chlorine, salt and sediments from drinking water; it also gets down to the molecular level and separates bacteria. It has to be very selective in what it removes. Undesirable constituents will clog the membrane over time and need to be removed from the system and the membrane itself.

Spiral-wound and hollow-fiber MF membranes are the two most common types of membrane used in reverse osmosis. Membranes are manufactured with a polymeric or ceramic material that must be mechanically strong to provide structural integrity and have some resistance to thermal and chemical attack. The membrane must be resistant to oxidants, acids and bases that are normally found in the raw water that it treats.

After the membrane is manufactured, it needs to be characterized to determine its properties. This includes knowing its pore size and function group as well as its material properties. This information is important to the selection of the correct membrane for a given application. In addition, the characterization is necessary for determining when it will need to be cleaned. Membrane fouling causes a reduction in membrane permeability and rejection. There are different kinds of fouling such as internal fouling, external fouling and concentration polarization fouling.

Flow Rate

When a reverse osmosis system is operating correctly, it produces a steady flow of clean water. However, the amount of water an RO system can produce depends on a few factors, including the flow rate. If you notice that the flow rate slows down, check your filters to make sure they’re not clogged. If the problem is a clogged tank bladder, you’ll need to replace the tank itself.

The flow rate of a reverse osmosis system can also be affected by the size and material of the membrane. The more membrane surface area, the higher the flow rate will be. A larger membrane will also have a higher pressure drop, so it requires more pressure to force water through it.

In the reverse osmosis process, water molecules move across a semi-permeable membrane against osmotic pressure. The more concentrated side of the membrane will have a natural tendency to migrate toward the less concentrated side. This is because of the balance of chemical potential energy.

When a reverse osmosis water filter is working properly, the flow rate of the reject water will be proportional to the net driving pressure differential across the membrane. For this reason, it is important to test the performance of the membrane at a specific temperature and pressure. For optimal performance, the membrane should be tested at 65 psi and 77 degrees Fahrenheit.