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Posted by on Jan 20, 2014

Reverse Osmosis vs. Selective Filtration – What’s the Difference?

As consumer awareness of contaminated tap water increases, many are looking for water filtration solutions. With many to choose from, it is important to understand the benefits and limitations of the different types of water filtration solutions available.

Here at Aquasana, we are often asked about the difference between reverse osmosis purification systems and selective filtration systems. While both are effective at removing contaminants, the filtration processes are indeed different and there are things you need to know about making an informed decision before your final purchase.

Reverse Osmosis

Reverse osmosis (RO) is a process of separation that uses water pressure to force the source water through a semi-pervious membrane that retains the solid contaminants on one side while allowing water to pass on to the other side. This membrane is effective at removing anything that is bigger than a water molecule. This process takes place through ion exclusion, where a concentration of ions emerges from a barrier at the membrane to allow water molecules to pass through without letting the contaminants do so. A typical reverse osmosis system will provide approximately 10% purified water, leaving the other 90% as wastewater. Because of this, reverse osmosis systems require a drain. In practical terms, this means it takes 10 gallons of water to make 1 gallon of filtered water.  The remaining 9 gallons is wastewater.

The reverse osmosis process removes fluoride, sodium, sulfate, nitrate, iron, zinc, mercury, lead, arsenic, chloride, and cyanide, along with a few other water contaminants. Because RO systems are effective at removing solids from water, they also demineralize the treated water. RO systems remove healthy minerals such as calcium, potassium, and magnesium. Without these minerals present, the water can become acidic. Some reverse osmosis systems can be equipped with a re-mineralization system to add back in healthy minerals and balance pH.

Selective Filtration

Many filters use carbon filtration technology to retain contaminants inside the carbon substrate preventing them from flowing through for consumption. Through the process of absorption, contaminants collect on a large surface area where molecules exert force for other molecules to attract to. The longer the water stays in contact with the carbon, the more contaminants can be absorbed from the water.

 Aquasana’s Claryum selective filtration technology uses 4 different filtration technologies to tackle contaminants in unfiltered water.  Activated carbon, catalytic carbon, ion exchange and 0.5 micron mechanical filtration technologies combine to form Aquasana’s Claryum Selective Filtration. The activated carbon reduces organic chemicals while the catalytic carbon targets chlorine and chloramines specifically. The ion exchange process filters heavy metals like lead and mercury and the 0.5 micron mechanical filter captures asbestos and chlorine resistant cysts like cryptosporidium and giardia, making the water safe to drink.

 Aquasana selective filtration is effective at removing over 96% of chlorine and chloramines, and over 99% of lead and mercury.  Additional contaminants the system is tested and certified to reduce include: herbicides, pesticides, cysts, asbestos, volatile organic chemicals (VOCs), pharmaceuticals, and a long list of additional water contaminants from the water while leaving in beneficial minerals such as calcium, magnesium, and potassium. These filters also minimize water waste on the environment.

NSF Standards  

Before making a purchase, it is important to know the health benefits of any drinking water system. It should pass NSF/ANSI standards including NSF #42 for aesthetic effects and NSF #53 for health effects.  NSF standard 42 establishes a minimum requirement for the point-of-use systems to reduce aesthetic contaminants such as chlorine, chlorine taste, odor, and particulates that may be present in drinking water. NSF standard 53 sets the parameters for POU systems designed to remove health-related contaminants such as lead, mercury, Cryptosporidium, Giardia, volatile organic chemicals, methyl tertiary-butyl ether, and other harmful contaminants from drinking water. Note that the NSF 53 certification does not mean that all of these contaminants are tested – manufacturers can choose any of them to test to get this certification, so be sure the list includes VOCs, lead, mercury and any other elements you want to ensure your filter tackles.

System Pros vs. Cons

Pros

Cons

Reverse Osmosis

Fluoride reduction

Arsenic reduction

Sediment reduction

Wastewater

Eliminates minerals

Unstable pH

Drainage system required

Results in acidic water

Oxidation reduction

No VOC reduction

Taste

Claryum Selective Filtration

Chorine & chloramine reduction

50+ other contaminants removed

Healthy minerals

Balanced pH

Low maintenance

Taste

No fluoride reduction

No nitrate reduction