What is Reverse Osmosis?

Reverse osmosis is one of the most effective water filtration systems on the market. It is incredibly energy-efficient, produces water on demand and removes toxins.


However, it also wastes some water and removes healthy minerals from your drinking water. Fortunately, there are a number of ways to avoid these drawbacks.

What is Reverse Osmosis?

Reverse Osmosis is a filtration technology that uses pressure to separate water molecules from contaminants. The process is similar to osmosis, which occurs naturally when solutions are separated by semi-permeable membranes. Osmosis pressure is a result of the concentration of solute particles on one side of the membrane being higher than that of the solvent on the other. Reverse osmosis applies more than osmotic pressure to water, pushing the solution away from the pressurized side of the membrane and toward the unpressurized side. This causes the solvent to move in a direction opposite that of the osmotic pressure and resulting in water passing through the membrane while contaminants are rejected.

The RO membrane removes bacteria, salts, sugars, proteins, particles, heavy metals (aluminum, arsenic, barium, cadmium, copper, lead, mercury, nickel, silver, and zinc), dissolved minerals, fluoride, chlorine, and other volatile organic compounds that produce unpleasant taste, odors, and colors in water. It also removes most microorganisms such as cryptosporidium and giardia, and all but the most resistant inorganic chemicals, including cyanide and asbestos.

Reverse osmosis is used in many industries and applications to make a wide variety of products. For example, orange juice concentrate is processed by reverse osmosis to reduce the cost and time required for heat-treatment. It is also used to make whey protein powder and milk concentrate, concentrating the whey from 6% to 10-20% solids before ultrafiltration processing.

How Does Reverse Osmosis Work?

In reverse osmosis, water is pushed through the semipermeable membrane by external pressure. This reverses the natural osmotic process of water passing through a membrane from a lower concentration to a higher concentration, which requires no energy because it is an innate part of the water molecules’ behavior. The membrane blocks the majority of contaminants including dissolved salts, organics, and bacteria as well as larger sediment particles and chlorine.

The microscopic pores on the membrane filter allow only pure water to pass through and collect the other contaminants and flush them away. The process is so effective that reverse osmosis is used in large scale desalination plants to produce drinking water from seawater.

One downside to the process is that it is an expensive way to produce drinking water for homes. Many reverse osmosis systems waste between 3 and 20 times as much water as they produce, and the system is also prone to clogging.

To counter this, many RO systems are installed with a first cartridge that filters out larger sediment particles and dissolved solids to protect the membrane. Another advantage of reverse osmosis is that it can recycle the high pressure pumps that push the water through, so some energy is re-harvested from the process. The water sludge that is produced by the system can also be redirected back across mineral beds to add beneficial minerals back to the water.

What Contaminants Can Be Removed by Reverse Osmosis?

Reverse Osmosis is a powerful filtration technology capable of reducing many contaminants found in drinking water. A reverse osmosis system can remove most EPA-regulated contaminants, including lead and asbestos; all cancer-causing radionuclides; 82 common chemical pollutants; pesticides and herbicides, such as Endrin, Lindane, and Pentachlorophenol; and the gasoline additive MTBE.

RO is also effective at removing particulates like rust, dirt, sand, and sediment that give drinking water a cloudy appearance and taste. Culligan RO systems can filter particulates down to 1 micron in size.

The process works by forcing pure water through the membrane using pressure differences. This natural osmotic process is known as reverse osmosis. The osmotic pressure forces chemicals from the more concentrated side of the membrane to the less concentrated side, where they are washed away as wastewater. Treated drinking water collects in a storage tank while rejected contaminants are flushed to a drain.

It is important to understand that a standard reverse osmosis unit wastes about 3 gallons of water for every gallon it produces. This wastewater contains the rejected contaminants and should be disposed of properly. For this reason, a reverse osmosis system should be paired with a carbon filter for maximum effectiveness and minimum wastewater production. The most effective way to determine if a reverse osmosis system is right for you is to start with a water test.

What Are the Benefits of Reverse Osmosis?

One of the biggest benefits is that reverse osmosis removes many harmful contaminants from water. It also improves taste and odor, saves money on bottled water costs, makes foods cooked with water look and taste better, and reduces energy usage compared to other types of filters.

Reverse osmosis systems are relatively inexpensive to purchase, install and maintain. They produce a large amount of highly purified water and can fit conveniently under your sink. They do require periodic filter replacements and use a lot of water waste, but this is offset by their effectiveness and energy efficiency.

The membrane is semi-permeable, meaning that dissolved substances with a positive charge are rejected and remain on the pressurized side of the membrane while pure solvent molecules pass through. Reverse osmosis is a great option for people with severe water contamination, but for most households it’s not necessary.

Those looking to get the most out of their reverse osmosis system should invest in a pre-filter and postfilter. Sediment and carbon filters remove the dirt, stone, larger organic materials and other visible impurities that may still be floating in your water. Postfilters reduce a wide range of chemicals, including volatile organic compounds, chlorine and other contaminants that cause foul odor and taste. These types of filters are often paired with a reverse osmosis system to ensure that you’re getting the best possible water for your health and wellbeing.