Reverse osmosis (RO) systems are among the most advanced and effective solutions for water purification, trusted to remove up to 99% of hundreds of contaminants, including heavy metals, PFAS ("forever chemicals"), microplastics, and microorganisms. According to the U.S. Environmental Protection Agency (EPA), point-of-use reverse osmosis systems are highly effective at reducing a wide range of drinking water contaminants, making them a reliable choice for home water treatment.
If you're asking yourself, what does reverse osmosis remove, you've come to the right place. This guide delivers everything you need to know about how this powerful water filtration system works to protect your family’s health and improve your home’s water quality. We’ll explore the specific impurities an RO system targets, what it might leave behind, and how you can get the best and purest drinking water possible from your tap.
What Is Reverse Osmosis?
Reverse osmosis (RO) is a highly effective water purification technology that uses a specially designed semi-permeable membrane to filter out impurities from drinking water. This membrane acts like a microscopic sieve, allowing only pure water molecules to pass through while blocking ions, molecules, dissolved salts, heavy metals, bacteria, and larger particles. The size of the pores in the membrane is incredibly small—about 0.001 microns, which is thousands of times smaller than a human hair. Because of this, RO systems can remove a wide range of contaminants, making the water safer and cleaner for consumption.
How Does Reverse Osmosis Work?
Before we look at what an RO system can remove, it helps to understand how the process works. Imagine a screen with microscopic holes—so tiny that only pure water molecules can get through. That’s the basic idea behind a reverse osmosis membrane.
The reverse osmosis process uses your home’s water pressure to force water through this special, semi-permeable membrane. The contaminants are flushed away in a waste stream, leaving pristine, purified water on the other side.
Modern reverse osmosis water filtration systems are more than just a single membrane. They typically include several stages to provide comprehensive water treatment:
- Sediment Pre-Filter: This initial stage captures larger particles such as dirt, sand, rust, and silt. Its main purpose is to prevent clogging and protect the more sensitive filters downstream, ensuring the system functions efficiently and lasts longer.
- Carbon Pre-Filter: This is where the question often arises—does reverse osmosis remove chlorine? The answer lies in this stage. The carbon pre-filter is specifically designed to remove chlorine and chloramine, along with volatile organic compounds (VOCs) and other chemicals. This step is critical because chlorine can degrade the reverse osmosis membrane over time and also contributes to unpleasant tastes and odors in tap water.
- Reverse Osmosis Membrane: At the heart of the system is the semi-permeable membrane, which removes up to 99% of total dissolved solids (TDS), including heavy metals like lead, arsenic, fluoride, nitrates, and even some microorganisms. This is where the true separation of pure water from harmful contaminants takes place.
- Polishing Post-Filter: Finally, the filtered water passes through a post-carbon filter, often referred to as a polishing stage. This final step enhances the taste and ensures any residual impurities are removed, leaving you with clean, crisp water ready for drinking or cooking.
Thanks to this layered, systematic design, modern reverse osmosis systems not only eliminate harmful substances but also directly address common concerns like “does reverse osmosis remove chlorine”, making them one of the most effective and popular choices for home water purification today.
What Does Reverse Osmosis Remove? (Comprehensive Overview)
So, what does an RO system do? A reverse osmosis system is exceptional at reducing a vast range of contaminants found in both municipal tap water and private well water. The effectiveness of a system can remove these impurities is often measured in a "rejection rate," which is typically very high.
Below is a comprehensive chart detailing the common contaminants an RO filter tackles, with data-backed removal rates.
| Contaminant Category | Example Contaminants | Typical % Removal | Health Risks (if present) |
| Heavy Metals | Lead, Mercury, Arsenic, Cadmium, Chromium | Up to 99% | Neurotoxicity, cancer, kidney and liver damage. Lead is a major concern in homes with old plumbing. |
| Total Dissolved Solids (TDS) | Sodium, Chloride, Sulfate, Calcium, Magnesium | 95–99% | High TDS can cause an unpleasant taste, scale buildup in pipes and appliances, and potential health issues like hypertension. |
| Microorganisms | Bacteria (E. coli, Salmonella), Viruses, Protozoa (Giardia, Cryptosporidium) | >99% | Gastrointestinal illness, serious infections, and other waterborne diseases. The membrane is a physical barrier. |
| PFAS ("Forever Chemicals") | PFOA, PFOS, and other perfluoroalkyl substances | Varies, high (%) | Hormone disruption, immune system effects, increased cancer risk. Look for certified systems for PFAS removal. |
| Nitrates & Nitrites | Nitrate, Nitrite | 92–98% | Blue baby syndrome in infants, cardiovascular health risks in adults. Often found in agricultural runoff. |
| Pharmaceuticals | Hormones, Antibiotics, Antidepressants | High (Varies) | Potential for hormonal imbalances and contributing to antibiotic resistance. |
| Microplastics | Most types and sizes | >99% | Health effects are still being studied, but there is concern about potential toxicity and inflammation. |
| Pesticides & Herbicides | Atrazine, Glyphosate, DDT | High (Varies) | Linked to cancer, endocrine disruption, and developmental problems. |
| Disinfection Byproducts | Chlorine, Chloramine, Trihalomethanes (THMs) | High (with carbon) | Can cause poor water taste and odor. THMs are known carcinogens. The carbon filter stage is key here. |
| Radionuclides | Radium, Uranium | High | Increased risk of cancer and damage to kidneys and other organs. |
Key facts to consider:
A properly functioning reverse osmosis filtration system readily removes all manner of particulate contaminants like clays, silts, and microorganisms. It also has high rejection rates of 95–99% for monovalent and divalent ions as well as heavy metals. This makes it one of the most complete water purification methods available for residential use.
Deep Dive: Most Searched Contaminants
Now that you’ve seen the complete list of contaminants RO systems can remove, let’s take a closer look at some of the impurities people are most concerned about. Understanding what does reverse osmosis remove in these specific cases can provide great peace of mind.
- Lead & Heavy Metals: Does reverse osmosis remove lead? Absolutely. It is one of the most effective methods, removing up to 99% of lead from household water. This is critical for homes with older plumbing or in areas with known contamination in their water supplies. Metals like arsenic and mercury are also effectively removed.
- Microorganisms: Does reverse osmosis remove bacteria and viruses? Yes. The pores in a reverse osmosis membrane are too small for most bacteria, viruses, and protozoa to pass through. This makes an RO system a powerful defense against waterborne illnesses, providing safe and clean water even when the source water quality is questionable.
- PFAS (“Forever Chemicals”): Does reverse osmosis remove PFAS? Yes, they are highly effective. Due to growing health concerns and increased regulation around PFAS, many are looking for a reliable water filter. A reverse osmosis water filtration system with an NSF/ANSI 53 or 58 certification is verified to dramatically reduce these harmful chemicals from your tap water.
- Microplastics: These tiny plastic particles are being found everywhere, including in our water bottles and tap water. The good news is that the fine pores of an RO membrane are extremely effective at blocking them. Independent testing confirms that reverse osmosis technology provides near-complete removal of microplastics.
- Chlorine: A common question is: does reverse osmosis remove chlorine? While standard RO membranes aren't very effective against chlorine, most residential RO systems include a carbon pre-filter that removes chlorine before the water reaches the membrane. This combination helps ensure both taste and safety.
- Fluoride: Many municipalities add fluoride to water for dental health, but some people prefer to remove it. Reverse osmosis is one of the few residential water treatment methods that can effectively remove fluoride, typically reducing it by 90% or more.
What Reverse Osmosis Does Not Remove
While a reverse osmosis water filter is a powerhouse, it’s not perfect. There are some limitations to be aware of. Understanding these helps you choose the right complete water system for your needs.
| Contaminant / Limitation | Why It's a Limitation | Alternative Solutions |
| Some Volatile Organic Compounds (VOCs) | Certain small chemical molecules like some solvents can pass through the RO membrane. | A high-quality activated carbon filter stage (usually included in RO systems) is essential for trapping these chemicals. |
| Certain Pesticides & Herbicides | Varieties with a very low molecular weight may not be fully blocked by the membrane alone. | Again, a robust carbon filter is the best solution and works hand-in-hand with the RO membrane. |
| Dissolved Gases | Gases like radon and hydrogen sulfide (which causes a rotten egg smell) can pass through the membrane. | Aeration systems or specialized carbon filters can target and remove these gases before they reach the tap. |
| Beneficial Minerals | The membrane doesn't distinguish between good and bad dissolved solids. It removes healthy minerals like calcium and magnesium along with harmful ones. | A remineralization filter can be added as a final stage to the RO system. This restores a balanced amount of healthy minerals. |
This table highlights the limitations of reverse osmosis (RO) systems when it comes to filtering certain substances. While RO membranes are highly effective at removing many contaminants, they are less efficient at filtering some volatile organic compounds (VOCs), certain pesticides, herbicides, dissolved gases, and even beneficial minerals. These limitations arise because of the small molecular size or gaseous nature of these substances, allowing them to pass through the membrane. One of the most frequent comments from new users is that the water taste is "flat" or "bland." This is a direct result of the mineral stripping effect. A remineralization cartridge is a popular and recommended addition to restore a more natural, pleasant flavor and add health benefits back to your filtered water.
Factors Impacting RO System Removal Efficiency
Not every reverse osmosis water system performs identically. The efficiency of reverse osmosis can be affected by several key factors.
- Source Water Quality: The water coming into the system matters. Water with extremely high levels of Total Dissolved Solids (TDS), an unusual pH, or challenging contaminants like high iron will put more stress on the system. In these cases, a higher-quality membrane and more robust pre-filters are needed for optimal results.
- System Design: The number and type of filtration stages make a big difference. A simple three-stage system is good, but a five or six-stage system with pre-filters, the RO membrane, a post-filter, and maybe even a remineralization filter will offer broader protection and better-tasting water.
- Maintenance: This is perhaps the most important factor. If you don't change the filters on schedule, they will become clogged. A fouled membrane won't just stop working; it can reduce the amount of water produced and may even allow contaminants to pass through. Regular maintenance is key to getting high-quality water. Neglecting filter changes can also put strain on the system’s pump and components, leading to costly repairs or a shorter system lifespan. To ensure consistent performance and clean, safe water, always follow the manufacturer’s recommended filter replacement schedule.
Is Reverse Osmosis Drinking Water Safe and Healthy?
This is a common and important question. Is water that has been stripped of nearly everything good for you long-term?
- Potential Drawbacks: The primary drawback of reverse osmosis water is that it’s demineralized. While we get most of our minerals from food, water can be a useful source. Removing minerals like calcium and magnesium affects the water taste and, for some, its nutritional profile.
- Taste: As mentioned, many users find the taste of pure RO water to be flat. Adding a remineralization filter is a simple fix that restores a crisp, refreshing flavor that many people prefer to both tap water and bottled water. These filters reintroduce essential minerals like calcium and magnesium, which not only enhance the taste but also offer additional health benefits. As a result, remineralized RO water often becomes the go-to choice for hydration, cooking, and even brewing coffee or tea.
- Health: Leading health organizations like the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC) agree that reverse osmosis drinking water is safe. For most people, the minerals lost from water can be easily obtained from a balanced diet. However, for long-term use, especially for infants or individuals on restricted diets, remineralization is often recommended to ensure a balanced intake of essential minerals. The top priority is to remove contaminants; adding minerals back is a secondary enhancement.
How to Choose the Best Reverse Osmosis System
Ready to enjoy the benefits of pure water? Here’s how to select the best reverse osmosis system for your home.
- Read Your Local Water Quality Report: Your municipal water supplier is required to provide a Consumer Confidence Report (CCR). This report lists the contaminants found in your local water. Knowing what you need to target helps you choose the right water filtration system. If you have well water, get it tested by a certified lab.
- Check for Certifications: Look for seals from third-party organizations like the NSF (National Sanitation Foundation). NSF/ANSI 58 is the standard for reverse osmosis drinking water treatment systems, and NSF/ANSI 53 certifies for specific health-related contaminants like lead and PFAS. This certification ensures the system works as advertised.
- Consider Your Needs: Think about your household size and daily gallons of water usage. This will help you choose a system with the right production capacity. Also, consider any special water quality issues you want to address, like hardness or specific chemical tastes. Many companies offer online tools to help you find the perfect fit for your home's water.
- Expert Insights & User Stories
The data is clear, but real-world stories show the true impact. Consider a family living in an older home with plumbing from the 1950s. Worried about lead exposure, they tested their tap water and found levels that exceeded the EPA's action level. After installing a certified reverse osmosis drinking water system under their kitchen sink, they had their water re-tested. The results were dramatic: the lead level dropped from 18 parts per billion (ppb) to less than 1 ppb. This simple change gave them confidence that the water their children were drinking was safe.
This is a common story. People across the country use reverse osmosis technology to solve problems ranging from high nitrate levels in rural areas to the unpleasant taste of chlorine in city water, confirming both its performance and the peace of mind it brings.
FAQs
Let’s clear up some common questions and misconceptions about what reverse osmosis can remove.
1. What is not removed by reverse osmosis?
Reverse osmosis is really great at getting rid of heavy metals, fluoride, nitrates, and microbes that are contaminants in the water. But like hydrogen sulfide, methane, radon, these gases dissolved in the water, either too small, or do not react with other things, reverse osmosis membrane can not stop them, only let them stay in the water. If you don't add another filter to deal with them, these gases will make the water give off an unpleasant odor. Moreover, when a reverse osmosis system purifies water, it removes calcium, magnesium, potassium and other minerals that are beneficial to the human body. While this makes the water purer, it makes the water taste less flavorful, and people get less minerals from the water. But then again, as long as you are not picky about what you eat and have a balanced nutritional profile, the impact of this is basically negligible to your health. The good news is that many reverse osmosis systems have been improved with activated carbon pre and post filters, so they can deal with those pesky gases. Some systems are even more thoughtful, adding a remineralization step to add back those essential minerals, so the water tastes better and has a more appropriate pH level. So, reverse osmosis itself is very strong, but if you can match with other filtration devices, you can solve the problem that the membrane can not deal with.
2. What can be removed by reverse osmosis?
Reverse osmosis (RO) water purification technology is definitely the most reliable solution for drinking water nowadays! It filters out 99% of the harmful substances in water. Those heavy metals, like lead, mercury, arsenic, even a tiny bit can be harmful to your health, but reverse osmosis systems are especially good at dealing with them. Whether it's city tap water or country well water, this system can get rid of the nasty stuff like nitrates and fluoride. If you pair it with an activated carbon filter, it can take care of even the toughest PFAS permanent chemicals, the pungent chlorine odor, and all sorts of volatile organic compounds. You should know that these can be the main culprits of cancer and endocrine disruption. Even better, it filters out invisible microplastics, drug residues, and bacterial viruses hidden in the water.
3. Are there benefits to drinking reverse osmosis water?
There are really so many benefits of drinking reverse osmosis purified water! First of all, it's like a super bodyguard, it can stop all those bad things in the water - lead, mercury and these heavy metals, the unpleasant smell of chlorine, and cancer-causing PFAS chemicals, and even bacteria and viruses can't escape. Think about it, 99% of the harmful substances are filtered out, no longer need to worry about drinking bad stomach or long-term accumulation of toxins to harm the body. The best thing is, reverse osmosis treated water tastes especially refreshing, especially with the addition of calcium and magnesium remineralization of the kind of water than tap water is too good to drink. Many people drink several cups more without realizing it, and their skin gets better, their digestion is smoother, and their whole body is more energetic. And with it, basically do not have to buy bottled water, both to save money and environmental protection, a year can make a lot less plastic waste it! Although reverse osmosis will filter out some minerals, but now advanced water purifier will be in the back to make up back, both safe and nutritious. Turn on the faucet every day to drink such clean water, really will make the quality of life a big step up. It's not just about drinking water anymore, it's like buying a health insurance policy for the whole family!
4. Which water filters can remove PFAS?
High-performance filtration systems are needed to get rid of PFAS in water. Perfluoroalkyl and polyfluoroalkyl residues in water are extremely harmful and can lead to cancer, reduced immunity and developmental problems. Of all the filtration options, reverse osmosis with activated carbon filtration is the most reliable. A reverse osmosis system works simply by passing water through a semi-permeable membrane. This allows the reverse osmosis system to keep out contaminants like PFAS. However, the molecular size and structure of PFAS are different, so the membrane alone cannot fully realize the filtration. This is where the addition of a granular activated carbon or carbon block pre-filter is necessary to catch the smaller compounds and extend the life of the membrane. This type of filtration provides the best removal. When choosing a system, third-party certifications are so important to look at. Be sure to choose a filter that is certified to NSF/ANSI Standard 53 (for health effects) or Standard 58 (for reverse osmosis systems), especially one that claims to reduce PFAS. These certifications indicate that the product has been rigorously tested and can be used with confidence. Ordinary carbon filters only remove small amounts of PFAS, not large amounts. If you are concerned about long-term exposure to PFAS in your home, choose a certified reverse osmosis system with carbon filtration. This provides both peace of mind and real protection.
5. What is the purpose of an RO system?
The main purpose of a reverse osmosis system is to remove all sorts of contaminants that may be in the tap or well water, so that a person can drink water that is exceptionally pure, tastes good and is safe to drink. It is the final hurdle in water filtration in the home, getting rid of impurities that may have escaped through other filters. Relying on a semi-permeable membrane, the reverse osmosis system can filter out 99% of dissolved solids, heavy metals like lead and arsenic, as well as chlorine, nitrates, PFAS, fluoride, microplastics, and even some bacteria and viruses can be dealt with. So whether you have a problem with the water quality in your home, or you simply want to drink the purest water possible, it's perfect for you. In addition to the health benefits, many people prefer reverse osmosis-treated pure water, especially with the addition of the remineralization step, which adds back calcium, magnesium and these beneficial minerals for a better taste. And it reduces the formation of limescale from minerals, and appliances like coffee makers and kettles are protected. All in all, a reverse osmosis system ensures that your family has clean, consistent, and contamination-free water, which is a smart investment for long-term health and wellness.