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By: Tyler Gatewood on October 30th, 2020

What is Reverse Osmosis (RO)? [Definition + Examples]

If you want a water filtration system to take the taste and cleanliness of your water to the next level, look no further than reverse osmosis. If you’re wondering what exactly reverse osmosis is, then you have come to the right place. Here at Exell we’ve been in the water business for more than 80 years, and we’re more than happy to explain what it is, how it works and share the effectiveness of reverse osmosis systems in purifying water.

What Is Reverse Osmosis?

Reverse osmosis (RO), is a water purification process that uses a partially permeable membrane to remove ions, unwanted molecules and larger particles from your drinking water. 

Contrary to osmosis, which is a process where molecules pass from a less concentrated side to a more concentrate side, the water permeates through the membrane from the more concentrated side (more contaminants) to the less concentrated (fewer contaminants) side to create a cleaner product. 

How Do RO Systems Work?

Reverse osmosis works by using a combination of an RO membrane, a sediment filter, and a carbon filter. The small pores in the RO membrane work to block contaminants while allowing water molecules through. 

The sediment filter is used to remove smaller particulate matter, such as dirt and other solids, from your water. It essentially works like a net, scooping up all of the unwanted debris flowing through your water system. This type of filter, called a postfilter, is attached to the point where the water enters your home. Due to their limited function in removing only larger particulates, they do not remove trace pathogen elements, heavy metals, or VOCs. 

The carbon filter is used to not only remove sediment, but also other contaminants that cause unpleasant taste, odor, or colors in your drinking water. These filters, known as prefilters, contain activated carbon, which work as a bonding agent. 

As contaminated water passes through, the impurities become chemically bonded to the carbon, causing them to stick in the filter as the water works its way through. 

This filter is excellent at removing contaminants that bond to carbon, however this does not include elements such as Sodium

What Are the Stages of an RO System?

RO systems are made up of between 3-5 stages of filtration. Three-stage RO systems are generally used for water purification either on a large scale or for non-drinking purposes. Five-stage systems are mostly used for residential drinking water and are not intended for water that is needed in large quantities. 

3 Stage RO Systems

Carbon prefilter

This stage is designed to perform preliminary sediment removal in an attempt to protect the RO membrane. It also removes chemicals and impurities that affect the taste and odor of the water. 

The RO membrane

This stage performs a secondary particulate removal by using applied pressure to push the water through the semipermeable membrane.

Carbon postfilter

This stage performs one final sweep in the filtered water as it is entering its final destination. 

5 Stage RO Systems

Polypropylene sediment filter

This filter is designed to remove all solid substances from the water. 

Carbon prefilter

This is a charged carbon water filter, containing a negative charge to attract contaminants containing a positive charge. This positively impacts the taste and odor of the water

1-micron polypropylene water filter

This filter is designed to clean up even the smallest particles (anything above 1 micron) that went unfiltered in the previous two stages. 

RO membrane

This is the main filtration stage, hence the name. Its main function is to eliminate excessive amounts of minerals and metals by only allowing water molecules to pass through the membrane. 

Carbon postfilter

Similar to the 3-stage system, the carbon filter is installed to remove any remaining impurities in the water as it enters the home. 

What Contaminants Do RO Systems Remove?

RO systems are extremely effective at removing bacteria, viruses, chemical contaminants, and protozoa. These systems are also effective at removing fluoride, chlorine, heavy metals, and other various total dissolved solids (TDS).

While RO systems are one of the most effective ways to purify your water, they do not remove everything. Some common contaminants that these systems may miss include pesticides, fungicides, and herbicides, as well as some dissolved gasses.

How To Get An RO System Installed In Your Home?

Once you have decided that an RO system is the right choice for you and your family, one of our expert team members would be happy to help. 

First, we will perform a site survey, which is where we test your water with a TDS meter to help us gauge the total dissolved solids in your water supply. During the site survey, our team will also survey the layout of your home. This is a very important step because RO systems require connection to a drain line, since they separate the tap water into two streams, one of which must be flushed out. 

At Exell, we are here to answer any questions you may have about your water service needs. Once we have determined that your water is safe for consumption, we are ready to discuss our options that we have available