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What is Reverse Osmosis and How Does it Work?


Reverse osmosis (RO) is a comprehensive water filtration process capable of addressing more water quality issues than a common carbon water filter, like those found in standard pitcher filters or refrigerator filters. RO uses high pressure to force water through a reverse osmosis membrane and reduce the presence of undesirable substances and contaminants.* In a typical reverse osmosis system, this process is usually only one step of a multi-stage filtration solution.

Read on to learn more about reverse osmosis and what it can do for your drinking water.

How Does Reverse Osmosis Work?

As the name suggests, reverse osmosis is the opposite of a process that happens in nature: osmosis. During osmosis, water or another substance moves from areas with a low concentration of a secondary material (for example, salt) to high-concentration areas, passing through a semipermeable membrane on the way. Think of it this way: Each water molecule is essentially trying to dilute the other molecules.

In reverse osmosis, this process is backwards. A filtration system applies pressure to a highly concentrated solution, sending it through a semipermeable membrane to a lower-concentration area. The membrane prevents undesirable components, such as those that cause water problems, from passing through. The concentrated molecules stay on one side and the filtered solution or treated water stays on the other.

An easy way to picture reverse osmosis in action is through desalination — the process of removing salt from seawater to make it potable. Pressure is applied to the seawater, which has a high concentration of dissolved salt. The membrane blocks these salt molecules but allows the water itself to pass through.

This same process occurs in an RO filter system. Artificial pressure and a reverse osmosis membrane help remove minerals, substances and potential contaminants from your drinking water.

Looking Inside Reverse Osmosis Filtration Systems

Keep in mind that RO isn’t the only process that happens in a full reverse osmosis filter system. It’s generally just one step in water treatment.

In a typical setup, water first flows through a pre-filter to remove larger sediment particles including sand or dirt. Then, it passes through an activated carbon filter that reduces unpleasant tastes and odors, such as those caused by chlorine in drinking water.

In the actual reverse osmosis stage, water moves through a tightly woven membrane that separates the water from contaminants as small as a single atom. This phase can reduce up to 95% of total dissolved solids in your water. Advanced RO products may also include additional filtration stages depending on the system and the user’s needs.

What is Not Removed by Reverse Osmosis?

While multistage reverse osmosis systems can minimize contaminants such as chloramine, volatile organic compounds (VOCs) and “forever chemicals” (like PFOS and PFOA), not all of this filtration takes place specifically in the RO stage. That’s why advanced reverse osmosis systems are designed to address these potentially harmful components by using additional filtration layers beyond the standard RO phases. Examples include Culligan’s Advanced Post-filter, which targets viruses and bacteria, and the Total Defense cartridge, which is certified to reduce contaminants including:

  • Lead
  • Pharmaceuticals
  • Mercury
  • Chloramine
  • Pesticides
  • Volatile organic compounds (VOCs)

The bottom line is this: Reverse osmosis itself is a process, but a reverse osmosis filtration system is often a whole lot more. If you’re looking for more control over your drinking water, you want advanced, multistep filtration in a comprehensive RO system.

How Does Reverse Osmosis Compare To Other Water Treatment Options?

Reverse osmosis is one of many ways to treat your drinking water. However, it’s among the most powerful options available for treating an impressively wide range of issues. Not only that, but under-sink RO systems ensure that you have cleaner, great-tasting water on demand whenever you want.

Compare this to other options like tap water filters or filter pitchers. Tap filters offer similar convenience in that you don’t have to purchase single-use bottled water, but the filtration itself is fairly limited. Similarly, basic filter pitchers may reduce the impact of chlorine on your water’s taste and smell, but they are unlikely to help you with issues such as viruses, bacteria, arsenic and more.

A high-volume, comprehensive reverse osmosis system is perhaps the best way to ensure your water is cleaner, safer and great tasting. Plus, when you choose a well-designed system with long-lasting filters that don’t need to be replaced every six months – and don’t have to buy cases of single-use plastic bottles – RO systems could save you money in the long run, too.

What Is Reverse Osmosis Water?

Unlike other types of water — for example, mineral water — reverse osmosis water isn’t defined by what it does or doesn’t contain. The term also doesn’t describe water with a particular taste or texture.

Instead, RO water is simply water that’s been treated with an RO filtration system. Thanks to all the science behind this process, reverse osmosis water tastes pleasant and offers a welcome upgrade from tap water.

Some single-use bottled water is treated using RO processes. However, “reverse osmosis water” most frequently refers to drinking water that’s treated at home (or in some cases, commercially). In these instances, reverse osmosis water is available on demand, straight out of a faucet. It tastes great and can even improve the flavor of food or beverages prepared with it.

Of course, an RO filter system doesn’t just provide you with great-tasting water. It also can help ensure that the water your household depends on is cleaner and safer.

Water Tests: The Best Way To Determine Your RO System Needs

Whether you suspect that there are impurities in your water or just want a filtration system for peace of mind, the first step should always be having a professional water test.

In fact, water testing should be a big part of your home maintenance routine. Well owners in particular are encouraged to test at least annually and after significant events including floods and pipe work. No matter where your water comes from, you should also have a test if you notice changes in the taste, odor or appearance of drinking water.

Even if you think your water quality has been consistent for a while, a test can reveal things you may otherwise not have discovered. Not all problem water issues can be seen, tasted or smelled, so testing is always a crucial step.

Professional tests and consultations help you zero in on the appropriate treatment options for your particular needs. For example, a water expert might recommend an RO filter system for your drinking water and a whole home system to prevent iron stains on your tubs and sinks. Tests also tell you your water’s hardness levels and whether you need a water softener.

A Quick Guide To Reverse Osmosis Systems

The best RO water filter system for your home will depend on your water use needs, specific problems or concerns, space requirements and budget. Culligan offers a variety of reverse osmosis systems designed to offer flexibility and uncompromising quality.

  • Aquasential® Smart Reverse Drinking Water Filtration System: The Aquasential Smart RO filter system is certified to reduce 59 contaminants, plus 15 emerging contaminants, and offers up to seven stages of filtration and 14 filter options. Smart technology lets you track water consumption and contaminants reduced. You and your local Culligan team can also get notifications when filter changes or other service is needed, for added peace of mind. You can even see cost and plastic savings from reduced use of single-use bottled water.
  • Aquasential® Reverse Osmosis Drinking Water System: Get cleaner, safer water right from your kitchen sink with a system that’s customized to your home’s specific water needs. Certified to reduce 61 contaminants and 15 emerging contaminants, the system is designed for easy setup and maintenance. An optional monitor light on your faucet can indicate when it’s time to change filters.
  • Aquasential® Tankless Reverse Osmosis System: This unique tankless design delivers a virtually endless supply of high-quality water without taking up extra space. The advanced system with four stages of filtration provides over 600 gallons of cleaner, safer drinking water per day from a stylish faucet in your choice of finishes.

What Kind of Maintenance Is Required With a Reverse Osmosis System?

As with any water filtration solution, RO systems need periodic maintenance to continue operating at peak performance. In general, routine upkeep for reverse osmosis solutions includes replacing pre-filters, post-filters and RO membranes. With Culligan reverse osmosis drinking water systems, some filters can last up to two years. Additionally, smart sensors can let you know when components need to be replaced, so you’re not removing them too soon or too late. Many local Culligan dealers also offer ongoing service programs that make this maintenance easy and hassle-free.

Are There Rental or Financing Options for an RO System?

If you think a reverse osmosis system is the best way for you to treat your drinking water at home, it’s important to consider your financial options.

Fortunately, buying an RO system from a supplier isn’t the only way to go about it. If you rent your home or want to try out a reverse osmosis system before you commit to purchasing one, many suppliers will offer you a rental option. Some agreements even include bundled maintenance and support. You may also be able to explore rent-to-own options — just remember to check with your landlord ahead of installing any systems if you don’t own your home.

Additionally, if you know that owning a reverse osmosis system is in your future, ask about about financing options from your provider. That way, you can start to enjoy great-tasting water quickly while completing payments for the system over time.

Reverse osmosis systems are an affordable solution for households with a wide variety of needs, from longtime homeowners to first-time renters on a budget. Work with your supplier to discuss not only which solution is right for you, but which payment options best fits your circumstances.

Reverse Osmosis: A Step Forward for Your Drinking Water

Reverse osmosis is one of the most effective options for a water treatment system, allowing you to address a wide range of potential contaminants and problems. RO filtration can help provide a virtually unlimited supply of cleaner, great-tasting water — all while reducing your use of single-use bottled water and giving you more confidence in what you drink.

Your home’s specific water filtration requirements will depend on what’s present in your water, as well as the taste, odor and safety issues you want to address. To make sure you get the solution that’s best for you, a water quality test is the first step.

Schedule your free, in-home test and consultation today.


*Contaminants may not be present in your water.

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