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Everything You Need to Know About Reverse Osmosis Water


If you’ve ever heard someone mention “reverse osmosis water,” they’re talking about water that has passed through a filtration system with a specialized membrane. This method, called reverse osmosis filtration (or RO), is a reliable way to ensure that you have cleaner, safer, great-tasting filtered water on demand.

There’s plenty to know about reverse osmosis water, RO filtration and what you can expect from a home RO system. In this complete guide, we’ll cover questions such as:

  • What is reverse osmosis?
  • How does reverse osmosis work?
  • How does a reverse osmosis system work?
  • How is reverse osmosis different from filtration?
  • What are some common substances removed by reverse osmosis?
  • What is the best reverse osmosis system?
  • What is the lifespan of a reverse osmosis system?

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

What Is Reverse Osmosis Water?

Although reverse osmosis water might sound like some kind of specialty drink or maybe even a unique brand of bottled water, it’s just tap water that’s been filtered using the reverse osmosis process. Here’s a breakdown of the process and why it works:

What is Osmosis?

To understand reverse osmosis, you first need to understand its counterpart: osmosis.

Osmosis is a natural process that occurs in all cell-based organisms — plants, animals and even people. During regular osmosis, a diluted solution passes through a semipermeable membrane and flows into a more concentrated solution to equalize the concentration on either side.

One everyday example of this can be found in plant root systems. When roots have a lower concentration of water than the soil around them, they act as a semipermeable membrane and work to balance the water content — which, in turn, keeps the plant alive.

What Is Reverse Osmosis?

As its name implies, RO takes regular osmosis and reverses the process. RO is a type of water filtration that can reduce up to 99% of certain contaminants in water, including both larger particles and those that can’t be seen.* This is typically a multistage process that includes pushing the water through a specialized, semipermeable membrane as well as other types of filters. The end result is cleaner water for drinking, cooking and other regular uses.

Concerned about potential water quality issues? Learn more about common water problems and recommended solutions with our Water Solutions Finder.

How Does Reverse Osmosis Work?

Unlike osmosis, which is passive and can happen automatically, reverse osmosis requires an external force or pressure. This means that it likely doesn’t happen in nature and is generally only used in reverse osmosis water filtration systems.

Let’s take a closer look at the RO process:

  • Pressure is applied to a highly concentrated solute solution, such as saltwater, so it can pass through a membrane and turn into a less concentrated solution.
  • The membrane allows water to flow through but blocks larger molecules, such as contaminants.
  • The reverse osmosis process leaves higher concentrations of solute on one side and only the solvent, or filtered water, on the other.

How Do Reverse Osmosis Filtration Systems Work?

Reverse osmosis can help reduce unwanted minerals, salts, metals and other impurities in your drinking water. How comprehensive RO water filter systems are varies depending on the brand and design, but in general, they perform four key steps to help improve your water quality:

Step 1: Pre-Filtration

An RO system connects to tap water lines. Remember, RO needs an external force, so these systems use high-pressure pumps to propel water through various levels of filtration. At this stage, tap water is called “feed water.”

The feed water passes through a series of initial filters, such as sediment and carbon filters, before flowing into the reverse osmosis chamber. These early filters can address issues such as:

  • Sand
  • Rust
  • Large particles
  • Chlorine tastes and odors

Step 2: Reverse Osmosis

Here, the feed water is pushed through the reverse osmosis membrane. This tightly woven membrane, which looks virtually impermeable to the naked eye, acts as a barrier to contaminants. Water is pushed up against this RO membrane at pressure and, depending on the membrane’s weave, only a certain percentage of contaminants can pass through. In Culligan® RO systems, this high-capacity membrane can reduce up to 99% of substances.

Step 3: Specialty Filtration

At this point, some systems also add additional filtration stages to address contaminants that may not otherwise be addressed. These options can include specialty filters like Culligan’s Total Defense cartridge, which can deal with contaminants including lead, mercury, volatile organic compounds (VOCs) and more, and the Advanced Post-Tank Filter, which addresses viruses, cysts and bacteria.

Step 4: Drainage and Storage

The reverse osmosis system drains out any wastewater. Each RO system has its own efficiency, which means some will generate more wastewater than others; it’s best to find a high-efficiency system. Culligan’s Aquasential® Smart RO System is the world’s most efficient RO, 3 to 5 times more efficient than other leading reverse osmosis systems.**

The treated water is ready for drinking and cooking. It’s stored in the RO tank until it’s used (unless you have a tankless RO system).

Bonus Step: Polishing

Some systems go beyond RO filtration. When the tap is turned on, these systems provide a final polishing filter to make your water as crisp and fresh-tasting as possible.

What Substances are Reduced by Reverse Osmosis?

A high-performing RO solution can reduce many drinking water contaminants, adding to the numerous benefits of owning a reverse osmosis filtration system. Here are just a few examples of water quality issues an RO system may help address:

  • Lead
  • Arsenic
  • Chlorine
  • Mercury
  • Chromium
  • TDS (Total Dissolved Solids)

Keep in mind that the reverse osmosis process itself doesn’t necessarily remove all these contaminants. When you install an RO solution, you’re actually relying on a whole system of multi-stage filters that work together in addition to the reverse osmosis membrane. If you took just one stage from the process described above, you wouldn’t get the full benefit of a comprehensive RO water filtration system — which is why it’s important to find a comprehensive solution that includes all the right filters, cartridges and steps.

What is Not Removed by Reverse Osmosis?

Even the very best RO membrane may not be able to address drinking water concerns such as Perfluorooctane Sulfonate (PFOS) and Perfluorooctanoic Acid (PFOA) — man-made chemicals that have potential impacts on health. Some reverse osmosis water filtration systems may also struggle to reduce volatile organic compounds (VOCs) or chloramine. That’s why RO systems like Culligan’s Aquasential® ROs introduce additional levels of filtration that can address these issues.

How are Reverse Osmosis Systems Different from a Water Filter?

Although reverse osmosis is often called “RO filtration,” it’s important to know what that really means.

Remember that reverse osmosis itself isn’t a filter; it’s just a process. The RO membrane makes this possible, but it isn’t technically a filter, either. When someone says “reverse osmosis filtration,” they’re likely referring to the entire multistage process that takes place in most RO systems — and keep in mind that reverse osmosis is just one step.

Things get more interesting when you compare RO systems to other types of water filters. Simpler systems use activated carbon, while some incorporate other filter media as well. While carbon filtration can help you minimize the taste or smell of chlorine in your drinking water and address some other aesthetic water issues, it likely won’t be very effective in minimizing the presence of dissolved solids, arsenic, viruses and bacteria. RO systems, on the other hand, are one of the most effective ways to broad treat water for a wide variety of potential contaminants.

Take a look at how RO compares to other water filters:

Whole-Home Water Filtration

Whole-home water filters don’t generally have an RO component. They also treat all your home’s water, not just your drinking water. A whole-home filter typically uses specific types of media designed to address individual problem-water issues such as:

  • Chlorine
  • Sulfur
  • Iron
  • Sediment

Simply put, whole-home filters usually target specific water quality issues, while RO filters can address a broader range of potential problems.

Countertop Filters

A countertop filter is a much simpler, less comprehensive solution to common water quality concerns. It’s often good at targeting unpleasant tastes and odors; it may even handle contaminants such as chlorine and fluoride. However, with fewer filtration stages and no RO component, countertop filters aren’t typically a comprehensive solution for water quality issues.

Faucet Filters

Faucet filters are a common answer to drinking water worries, but their main benefit is their simplicity. For example, while they can often handle chlorine and sediment, they likely won’t touch lead. Meanwhile, a comprehensive RO system does all that and more.

Pitcher Filters

Pitcher filters may be one of the least efficient water quality solutions for many people. That’s not just because these systems are limited to simple filtration needs; it’s also because they only address small amounts of water at a time. With an RO system, the filtration is done for you, and you’ll always have fresh water on demand.

Fridge Filters

Fridge filters are generally effective for addressing chlorine issues, but they don’t get much further than that. If you want a more robust solution that handles a wider variety of potential contaminants, you need RO filtration.

What Are The Best Reverse Osmosis Systems?

When you’re ready to take control of your drinking water quality, you’ll find that RO systems come in all shapes and sizes. Here are a few tips on choosing the right one for your needs:

What to Look For in RO Filtration Systems

Not all RO systems are designed to be a full, comprehensive solution. Look for signs of high-quality design and user-friendliness, including:

  • Multiple stages of filtration: Reverse osmosis alone isn’t enough to tackle every water problem. For more robust filtration, you need a system with multiple filtration stages, including options for advanced filtration.
  • Smart features: Smart features help you get more from your system. For example, some help you track water usage, contaminant reduction, filter replacement and more. The best systems even have a smartphone app for real-time monitoring.
  • Certifications: Third-party certifications guarantee that a filtration system can efficiently and effectively address certain contaminants.
  • Service and support: Buy from a provider who offers service and support packages. Additionally, they should answer your questions, perform professional installation, recommend maintenance schedules and help simplify your water filtration experience.

The best way to choose an RO system is to have an in-home water test and consultation. These generally take under 30 minutes, and their goal is to reveal your biggest water quality issues. Your local water expert can interpret the results and help you choose the best reverse osmosis filtration system for your needs.

Best RO Systems

Culligan’s reverse osmosis systems are designed to make it easy for you to enjoy safer, cleaner water at home. Whether you want a virtually endless supply of RO water or your priority is a compact design that fits seamlessly into your home, we can help find the best system for you.

  • Aquasential® Smart Reverse Drinking Water Filtration System: The Aquasential Smart RO is the world’s most efficient,** certified to reduce 59 contaminants, plus 15 emerging contaminants. Smart technology lets you track water consumption and contaminants reduced. You can also get real-time alerts for filter changes and kitchen leaks, and enjoy proactive service through optional remote system monitoring by your local Culligan experts.
  • Aquasential® Reverse Osmosis Drinking Water System: Get an unlimited supply of cleaner, safer water with a system that’s customized to your home’s specific water needs. Certified to reduce 61 contaminants, the system is designed for easy setup and maintenance. An optional integrated monitor light on your faucet can indicate when it’s time to change filters, which can last up to two years.
  • Aquasential® Tankless Reverse Osmosis System: The unique tankless design delivers the quality water your home depends on without taking up extra space under your sink. The filtration system reduces dissolved solids in your water by up to 95%. Providing over 600 gallons of cleaner, safer drinking water per day, it’s a great solution for homes with high-volume drinking water needs.

What Is The Lifespan of a Reverse Osmosis System?

The lifespan of an RO filtration system depends on two key factors:

RO Maintenance

Like just about everything, reverse osmosis filtration systems require a little maintenance to remain effective. Luckily, there’s not much work required on your end. Your biggest job is to stay on top of filter and membrane replacement.

In Culligan RO systems, filters can last about one or two years, depending on the type you select, how much water you use and other factors, like your raw water quality. The RO membrane can last up to five years. Just make sure to keep a good schedule and replace these components regularly.

You should also sanitize the system about once a year for maximum performance and efficiency.


Selecting an RO system from a reliable manufacturer and service partner is important to help keep your system running efficiently and effectively. Culligan designs and manufactures its own systems and our experts are equipped to take care of everything for you. From installation to maintenance, we can help ensure the longevity of your RO system and keep all the parts working properly.

Reverse Osmosis FAQs

Want to learn even more about reverse osmosis systems and RO water? Check out these FAQs:

Is RO Water “Pure” Water?

Even in nature, water is rarely (if ever) completely “pure.” For example, rain often filters through rocks and picks up mineral content on its way to reservoirs, wells and other sources. While reverse osmosis filtration systems address many potential contaminants, even the best filter likely couldn’t create pure water.

Luckily, water doesn’t have to be pure to be good for your body. In fact, some mineral content — such as healthy calcium — can improve water’s natural taste and introduce potential health benefits (although this is still being studied).

Can You Buy RO Water?

Some brands of bottled water say they use reverse osmosis and other treatment techniques. Additionally, if you choose to subscribe to a bottled water delivery service, you may be able to have RO water delivered straight to your home or office (depending on which options are available in your area).

Installing an RO system at the point of use, however, ensures that you can enjoy the benefits of reverse osmosis water whenever you want. Once it’s up and running, all you have to do is turn on the faucet, and you’ll have great-tasting water straight from the kitchen sink for cooking, drinking or making beverages such as tea and coffee.

Is RO Water the Same as Distilled Water?

Although distilled and reverse osmosis water may sound similar, don’t make this common mistake. They’re actually two different things.

Distilled water is treated using a combination of evaporation and condensation to remove dissolved solids. It doesn’t use the same system of filters or rely on an RO membrane.

Both distilled and RO water are available commercially, but reverse osmosis is more commonly used in home treatment systems for drinking water. While some households occasionally choose to go with a home distillation solution, these options tend to be less convenient, and they can require a lot of energy and owner involvement to run.

Can You Have RO and a Water Softener?

Reverse osmosis systems and water softeners are two different water solutions. RO handles contaminants that may impact the taste, odor, appearance or quality of your water; meanwhile, a water softener removes hardness minerals such as calcium and magnesium.

The good news is that you don’t have to choose between filtration and softening. Because RO systems and water softeners don’t interfere with one another, you can address common contaminants and eliminate hard water problems at the same time.

Does RO Impact Your Water Heater?

Water heaters and reverse osmosis systems work separately. They’re generally installed in different parts of your home, too — which means you can have both without worry.

Does RO Impact Water Pressure?

A properly installed and functioning RO system shouldn’t significantly reduce your water pressure. If you notice issues, there could be a few explanations, including water line issues or filter clogs. Contact your local Culligan Water expert for help diagnosing and addressing these kinds of problems.

Can You Change the pH of RO Water?

Although there’s some discussion about whether water of different pH levels is actually better for you, one thing’s for sure: You should be able to customize your water experience.

That’s why Culligan offers the Mineral Boost cartridge, which adds natural calcium back to your water after the reverse osmosis process. This can enhance the taste and alkalinity of your water.

Better yet, this calcium doesn’t contribute to hard water. That’s because your RO system and the Mineral Boost cartridge are generally installed at the point of use — for example, your kitchen sink — and won’t impact the water going directly to your dishwasher, washing machine or bathroom faucets. For this reason, you can also have both a Mineral Boost cartridge and a water softener.

Can You Use RO on All Water?

Many people choose reverse osmosis systems regardless of where their water comes from.

For municipal water users, this is often due to the presence of chlorine. Water treatment plants use chlorine to decontaminate the city water supply, and while this is good news for health and safety, it can have an unpleasant odor or taste. Of course, other contaminants — such as copper from your home’s plumbing — can get into your water on its way to the tap, so reverse osmosis is a good way to address potential water quality issues.

For well water users, the choice is even easier. Because private wells aren’t treated or managed by the city, there’s centralized treatment step to address common contaminants — which means an RO system is a good way to go.

Enjoy Your Own Reverse Osmosis Water

A reverse osmosis system is a reliable, effective way to address many common contaminants, including those that may impact the taste, odor or appearance of your tap water as well as quality and contaminant concerns. With the best RO systems, a combination of robust filtration steps creates a comprehensive solution for your water quality.

Ready to enjoy filtered water on demand? Schedule your free, in-home water test and consultation to get started.


*Contaminants may not be present in your water.
**Efficiency is based on 3rd party testing to NSF standards.

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