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A reverse osmosis system provides highly pure and great tasting drinking water free from harmful contaminants – water that is much more pure than what other filter systems can provide.
Furthermore, the vast majority of reverse osmosis systems are perfectly suited for family use, they are easy to install and service, and they save you a whole lot of money that you would otherwise have to spend on bottled water.
So, here is our collection of the 8 best reverse osmosis systems. Towards the bottom of the page, you will find our detailed buying guide. Enjoy!
- 1 Best Reverse Osmosis Systems – Top Picks
- 2 Best Reverse Osmosis System Reviews
- 2.1 1. AquaTru Reverse Osmosis Water System
- 2.2 2. Aquasana OptimH2O Reverse Osmosis + Claryum
- 2.3 3. Waterdrop WD-G3-W Reverse Osmosis Water Filter System
- 2.4 4. Home Master TMHP HydroPerfection Reverse Osmosis System
- 2.5 5. RKIN Zero Installation Purifier Reverse Osmosis Water Filtration System
- 2.6 6. Review: SoftPro Green 5-Stage Reverse Osmosis System (High-Efficiency 75 GPD) by QWT
- 2.7 7. Crystal Quest Portable RO Filtration System
- 2.8 8. NU Aqua Platinum Series 5 Stage 100 GPD RO System
- 3 RO Filters Comparison Chart
- 4 Buyer’s Guide – How to Buy the Best RO System for Your Home
- 5 What is Reverse Osmosis Exactly?
- 6 How Do Reverse Osmosis Systems Work?
- 6.1 RO System Components and the Multi-Stage Filter Process
- 7 Reverse Osmosis Filtration System Recovery Rates
- 8 What Do Reverse Osmosis Filters Remove from Water?
- 9 Is a Reverse Osmosis System Worth It? – Advantages & Disadvantages
- 10 Does Drinking RO Water Pose a Health Risk?
- 11 Do I Even Need a Reverse Osmosis System?
- 12 How to Install an Under Sink RO System
- 13 Reverse Osmosis System Maintenance
- 14 Frequently Asked Questions (FAQ)
- 15 Conclusion
Best Reverse Osmosis Systems – Top Picks
Best Reverse Osmosis System Reviews
The order of the following reverse osmosis system reviews is deliberate. Our favorite products are at the top.
1. AquaTru Reverse Osmosis Water System
In our opinion, the best reverse osmosis system in 2021 is the AquaTru.
Most importantly, the AquaTru Reverse Osmosis Water System was tested and NSF-certified against multiple testing standards and has shown to remove more than 80 partially harmful contaminants from drinking water. And apart from offering a layer of protection for your health, water filtered with the AquaTru also tastes a lot better.
More pros are the quick 5-minute setup and the fact that system maintenance is simple and low-cost.
- Price: $$$
- Filter stages: 4
- Flow rate: System can produce 1 gallon of pure water in 10-15 minutes
- Estimated filter replacement cost per year: $120
- NSF: 42, 53, 58, 401, P473
- This countertop RO system doesn’t take up much space and is very easy to use.
- The 4-stage filtration process applies a sediment and activated carbon pre-filter which catches sand, rust, and other large suspended solids to prevent clogging of the rest of the system, as well as chlorine taste and odor (96.6%), and certain chemicals and organics. The reverse osmosis membrane rejects 93.5% fluoride, 99.1% lead, 97.2% hexavalent chromium, and 96.4% radium among other things. A coconut shell carbon block post-filter adsorbs 97.5% PFOA & PFOS, pharmaceutical drugs, pesticides, and VOCs.
- The AquaTru is certified by IAPMO according to NSF/ANSI Standard 42, 53, 58, 401, & P473 which guarantees its effectiveness.
- An internal pump increases water pressure which allows for a much faster filtration than usual. Also, the amount of produced waste water decreases to as little as 0.25 gallons per gallon filtered water thanks to the pressure pump. FYI: Most standard reverse osmosis systems waste 3 to 5 gallons of water per 1 gallon of purified water.
- The purified water collects in a tank – features one-button dispensing – which can be removed for storing in the refrigerator.
- The brine water is stored in a second tank and can be easily discarded.
- No skills or prior experience as a handyman are required for setting up this standalone system. The assembly doesn’t involve plumbing or drilling and barely takes 5 minutes. All in all, great for renters and to save money on professional installation.
- Filters last between six months and two years and are fast to replace without tools (the unit will tell you when). Replacement filter cost is affordable.
- Any plastic is free from BPA and BPS.
- A one-year warranty covers the whole reverse osmosis system.
- Some AquaTru RO systems have leaked due to a design flaw.
- For a small percentage of users, the system started to malfunction within several months of use.
2. Aquasana OptimH2O Reverse Osmosis + Claryum
In our opinion, the best under sink reverse osmosis system in 2021 is the Aquasana OptimH2O Reverse Osmosis + Claryum. Removing 88+ contaminants it not only provides high quality drinking water, the RO system also uses remineralization for well-rounded water taste and more balanced pH.
- Price: $$
- Filter stages: 4
- Flow rate: 0.5 gallons per minute
- Estimated filter replacement cost per year: $200
- NSF: 42, 53, 58, 401, P473
- 3 stages of filtration remove 97.7% chlorine and chloramine, 99.3% lead, 97.0% chromium 6, 97.6% arsenic 5, 95.7% fluoride, 96.0% PFOA and PFOS, 40% nitrate/nitrite, 99% asbestos, and dozens of other contaminants including heavy metals, volatile organic compounds, microorganisms, and chemicals like pesticides.
- The filter process which combines activated and catalytic carbon with an RO membrane is NSF-certified against Standards 42, 53, 58, 401, and P473 which substantiate the contaminant reduction claims.
- A fourth filter stage adds calcium, magnesium, and potassium into the filtered water. These healthy minerals add to your recommended daily intake and greatly improve taste.
- For the dispenser, you have the choice between chrome, brushed nickel, and oil-rubbed bronze.
- Do-it-yourselfers shouldn’t have any problem installing the reverse osmosis filtration system as long as they stick to the instructions provided.
- Maintenance is easy and doesn’t require much of your time. The different filter stages last between 6 and 12 months, the reverse osmosis membrane between 1 and 3 years.
- You can try the Aquasana OptimH2O during the 90-day money-back guarantee. If you’re not happy, you can return it for a full refund.
- A 2-year limited warranty covers defects in materials or workmanship in manufacturing.
- A few reviewers complained about leaking and the water dispenser being flimsy.
- The estimated annual filter replacement costs are comparatively high. You get a discount for joining Aquasana’s Water for Life filter program.
3. Waterdrop WD-G3-W Reverse Osmosis Water Filter System
In our opinion, the number one tankless RO system in 2021 is the Waterdrop.
No tank is perfect for people who have only little space left in their sink cabinet. Tankless design also means that water needs to be filtered on demand which is perfectly fine since the Waterdrop WD-G3-W Reverse Osmosis Water Filter System has a built-in booster pump.
- Price: $$$
- Filter stages: 3
- Flow rate: 0.3 gallons per minute
- Estimated filter replacement cost per year: $100
- NSF: 58
- Tankless RO systems require less space.
- A polypropylene cotton and activated carbon block composite filter, an RO membrane, and another coconut shell activated carbon block filter remove the common contaminants: Chlorine taste and odor, sediments such as sand and rust, heavy metals, bacteria and viruses, etc. In other words, fresh and great-tasting water perfect for drinking and cooking is guaranteed.
- The system is certified according to NSF/ANSI standard 58 for TDS reduction (94.0%).
- A pump boosts water pressure and ultimately filtration speed so that smaller and larger drinking vessels fill quickly. Another benefit of increased pressure is less water waste production, from around four gallons to no more than one gallon for each gallon you consume.
- The tankless under sink RO system is easy to install if you have the necessary tools.
- The water dispenser has a built-in filter life indicator so you don’t need to write down the date of the last filter replacement. As long as the LED light is blue the filters perform at their peak. Yellow light means you have less than 40 gallons of filtered water left. Red LED light indicates the filters have reached the end of their life and must be changed. You will also hear an acoustic signal when dispensing water.
- More LED lights are to be found on the unit’s front panel which also displays output water TDS. Both are useful if you want to check the current status and effectiveness of the filter system.
- There’s no need for tools and shutting off the water supply when replacing filters. Plus, the process literally takes less than one minute for changing all three filter stages.
- Waterdrop offers a 30-day product trial period.
- The product warranty covers the first year after purchase.
- Some users need to drain a full gallon of water before the Waterdrop WD-G3-W RO system reaches maximum TDS reduction.
- Additional NSF testing and certifications would have been nice.
4. Home Master TMHP HydroPerfection Reverse Osmosis System
For people on well water, the Home Master TMHP HydroPerfection Reverse Osmosis System is the best choice, because in addition to regular RO filtration it features UV light purification which inactivates 99.99% waterborne pathogens like viruses and bacteria.
- Price: $$$
- Filter stages: 9
- Filtering capacity: 75 gallons of water per day
- Estimated filter replacement cost per year: $150
- NSF: –
- A 5-micron sediment pre-filter, a 5-micron coconut shell catalytic carbon and KDF-85 pre-filter, the DOW FILMTEC membrane, UV filter, and a coconut shell granular activated carbon post-filter remove or reduce the following contaminants among others: Sediments, cloudiness, tastes, odors, chlorine, chloramine, arsenic, hexavalent chromium, lead, radium, iron, pesticides, hydrogen sulfide, and microorganisms.
- The full contact post-filter also replenishes the water with minerals for improved taste and alkalinity. Less acidic water also helps to prevent storage tank degradation.
- A permeate pump increases total daily water output while reducing waste water production (from four to one gallon for each gallon you can use). Higher water output also means fast flow from the dispenser.
- Written installation instructions + a detailed video series, color-coded tubing, and quick-connect fittings make installing the Home Master TMHP HydroPerfection Reverse Osmosis System as simple as possible.
- The filter stages have a modular design and last for a long time. This has two benefits: 1. When you replace one of the filter elements you discard the entire housing which prevents mold, bacteria, and algae from accumulating. 2. The filters can be replaced without tools and without closing the cold water line.
- The 30-day money-back satisfaction guarantee is rather short. However, the entire system is warranted for 5 years and customer support is great.
- Home Master RO systems are Made in USA, meaning they are slightly higher priced than usual.
- We are missing NSF/ANSI testing and certifications.
- Some people had problems with the DIY installation.
5. RKIN Zero Installation Purifier Reverse Osmosis Water Filtration System
Coupon Code (8% Off): WM8Percent
The RKIN Zero Installation Purifier Reverse Osmosis Water Filtration System is another standalone and installation-free model; a model that comes in two futuristic designs and that’s provides you with endless and great-tasting alkaline drinking water.
- Price: $$$
- Filter stages: 4
- Flow rate: System can produce 1 gallon of pure water in 10-20 minutes
- Estimated filter replacement cost per year: $70
- NSF: 58
- Super easy to use: Just fill the bottom tank with water and hit start.
- 4 stages of filtration – five-micron sediment filter, activated coconut shell carbon block filter, RO filter membrane, carbon and remineralization post-filter – remove up to 99.0 percent of water impurities, including sediment, chlorine, disinfection byproducts, bad taste and odor, and heavy metals. Your water will also be enriched with magnesium and calcium for better taste and alkalinity.
- Optionally, you can use the anti-scale carbon pre-filter if your water has high levels of hardness or general TDS which increases the overall service life of the subsequent filter stages.
- The RO filter system relies on a pump to increase water pressure for faster filtration and an improved water recovery rate (50%). The latter means less water, 50 percent to be precise, goes down the drain as waste water.
- The water tanks are BPA-free.
- Installation-free water filters are ideal for renters and if you don’t want to make any permanent changes to your plumbing. And they are much more convenient of course!
- Each filter element lasts at least one year and features a simple twist on/off mechanism or quick-connect fittings. What’s more, a warning light reminds you when it’s time for a filter replacement. Thus, system maintenance is a breath.
- You can try the ZIP for a full year. During this period you can return it for a full refund no questions asked.
- There’s a one-year limited warranty.
- The feed tank which is used to start the reverse osmosis process is known to cause problems with some systems.
- Only the membrane has an NFS certification for standard 58.
- We read different reports about leaking from different system parts.
6. Review: SoftPro Green 5-Stage Reverse Osmosis System (High-Efficiency 75 GPD) by QWT
At a fair price, the SoftPro GREEN Reverse Osmosis Water System removes 96% of up to 1,000+ contaminants found in residential tap water, says Quality Water Treatment. Let’s find out more!
- Price: $$
- Filtering Process: 5-stage reverse osmosis system
- Filtering capacity: 75 gallons per day
- Estimated filter replacement cost per year: $70
- NSF: –
- Rust and particles, bad tastes, odors, chlorine, lead, nitrates, chromium, arsenic, toxic heavy metals, organic impurities, fluoride, bacteria, viruses, and other dissolved solids are removed by the reverse osmosis drinking water filtration system. The 5-stage setup consists of one 5-micron sediment filter (multi-gradient depth), two 10-micron (nominal) block filters made of coconut shell activated carbon, a thin-film composite 75 gallons per day reverse osmosis membrane, and one activated in-line carbon post-filter.
- You can upgrade the post-carbon filter with an advanced alkalizing filter which raises the pH level to eliminate acidic water while adding beneficial minerals back into the water.
- The waste-pure water ratio is 1:1, meaning only one gallon of waste to one gallon made.
- Chrome, ivory, white, matte black, gloss black, venetian bronze, satin nickel – Quality Water Treatment provides 24 different lead-free faucet styles with the SoftPro Green. Choose your favorite for free to match your kitchen design. Simply email the company with your faucet style and color after placing your order.
- QWT is “committed to 100% customer satisfaction”. Therefore, you can return your purchase for a refund within 60 days after the shipping date if you are unsatisfied for any reason.
- The SoftPro Green RO water system carries a 5-year manufacturer warranty.
- We couldn’t find any information on specific contaminant reduction rates or testing/certifications to back the manufacturer claims.
7. Crystal Quest Portable RO Filtration System
How about the Crystal Quest Thunder as your next portable reverse osmosis system? It is our favorite model in the category! It can be connected to any standard kitchen faucet in less than a minute and is small enough to fit in your RV or suitcase in case you’re planning a trip.
- Price: $$
- Filter stages: 10
- Flow rate: 0.03 gallons per minute, 50 gallons per day
- Estimated filter replacement cost per year: $75
- NSF: –
- The Crystal Quest Thunder measures 16x7x7 inches – one of the most compact and portable reverse osmosis water filtration systems on the market.
- Water passes through 10 stages of filtration before it comes out the other end all nice and clean. Along the way, GAC, an RO membrane (50 gpd), Eagle Redox alloy, and ion exchange resin filter bad taste & odor, silt, sediment, 99.9% chlorine, THM’s, benzene, cryptosporidium, giardia, pesticides, herbicides, VOCs, lead, mercury, copper, nickel, cadmium, aluminum, and other metals and salts etc. In addition, the copper-zinc alloy inhibits bacterial growth throughout the entire unit.
- The filter stages are separated by 1-micron filter pads to prevent clogging.
- All standard-sized faucets are compatible. Adapters are part of the package.
- For maintenance, everything you need to do is quickly replace the granular activated carbon filter every 12-18 months and the semi-permeable membrane and SMART filter every 2-3 years.
- Product warranty is valid for one year.
- As with most portable RO filtration system water flow is slow. Tip: Fill a large container for later use.
- Unfortunately, the Crystal Quest Thunder has been tested nor certified against NSF standards. Contaminant reduction rates are provided either.
8. NU Aqua Platinum Series 5 Stage 100 GPD RO System
The main buying reason for the NU Aqua Platinum Series 5 Stage 100 GPD RO System is low price. Also, replacement filters are super affordable making the unit perfect for people on a small budget. By the way, shipping is free, too.
- Price: $
- Filtering Process: 5-stage reverse osmosis system
- Capacity: 100 gallons of water per day
- Estimated annual filter replacement cost: $50
- NSF: –
- Nu Aqua is the manufacturer of their own products so they can offer the best possible prices.
- 5 filter stages are combined into a single filter system. First, a one-micron polypropylene sediment pre-filter traps sand, dust, dirt, rust, and debris to protect the rest of the system from fouling. Filter 2 is a granular activated carbon filter taking care of chlorine, color, pesticides, and any remaining particles missed by the first filter stage. Stage 3 is a coconut carbon block filter reducing chlorine, chloramine, VOCs, heavy metals, and cyst. Now the thin-film composite RO membrane rejects salts, heavy metals, radioactive contaminants – you name it. And lastly, an inline activated carbon filter gives your water a final polish to assure the most pristine taste and smell.
- The high-flow membrane fills the water tank in as little as two hours which eliminates long waiting times.
- All parts are BPA-free to avoid recontamination.
- NU Aqua provides a written instruction manual and a DVD. DIYers can complete the installation within a few hours.
- According to NU Aqua, maintenance is a breeze. The sediment filter comes with a clear housing for easy monitoring. How often do you need to change filters? Every 6 to 9 months, depending on your water usage and quality. The semi-permeable membrane lasts up to one and a half years. Costs are minimal.
- The package includes a free TDS meter.
- A 180 days money-back guarantee brings peace of mind.
- Quite surprisingly, the NU Aqua Platinum Series 5 Stage 100 Gallons Per Day RO System is warranted for 5 years.
- People find the installation directions could do with some improvement.
RO Filters Comparison Chart
How do the best reverse osmosis systems perform when directly compared to each other?
|Reverse Osmosis Filtration Systems||$$$||Filter Stages||Water Production||NSF/ANSI||Best For||Details|
|AquaTru RO System||$$$||4||1 Gallon of Pure Water in 10-15 Minutes||42, 53, 58, 401, P473||Best Overall||Easy Installation Process, Fast Filter Changes, High Capacity System Includes Pump for Less Water Waste|
|Aquasana OptimH2O Reverse Osmosis + Claryum System||$$||4||0.5 gpm||42, 53, 58, 401, P473||Best Under Sink Water Filter for City Water||System Filters 88+ Contaminants, Faucet Included|
|Waterdrop WD-G3-W RO Unit||$$$||3||0.3 Gallon Per Minute||58||City Water||Filters Water on Demand, Faucet Include|
|Home Master TMHP HydroPerfection System||$$$||9||75 Gallons per Day||–||Best for Well Water||9 Stages of Filtration, 2x Pre-Filters (Sediment and Carbon Filter), UV Light, Permeate Pump, Fast Filter Changes, with Faucet, Excellent Customer Service|
|RKIN Zero Installation Purifier||$$$||4||1 Gallon of Pure Water in 10-20 Minutes||58||Municipal Water||Compact Unit, Installation-Free, High Capacity 4-Stage System Includes Pump for Less Water Waste|
|SoftPro Green 5-Stage Reverse Osmosis System||$$||5||75 gpd||–||High Capacity Filters|
|Crystal Quest Thunder System||$$||10||0.03 gpm, 50 gpd||–||Best for Portable Use||Quick Installation, Compact Design|
|NU Aqua Platinum Series Reverse Osmosis Filtering System||$||5||?||–||5 Stage Reverse Osmosis Water System, 100 Gallons Per Day|
Buyer’s Guide – How to Buy the Best RO System for Your Home
Here’s our buying guide with everything you need to know about how to buy the best reverse osmosis system.
Reverse osmosis systems can be categorized into three groups: Under sink reverse osmosis systems, countertop reverse osmosis systems, and whole house RO system setups.
You’re most likely eyeing with the first or second type that, every day, give you access to filtered water meeting drinking water quality standards at one faucet in your home. In most cases, a whole house RO system is a bit over the tip for residential use.
The difference between under sink and countertop RO systems is that the former require proper installation, which includes drilling a hole in your kitchen counter and establishing a drain connection. Most countertop units are different. They are installation-free which is great if you can’t or don’t want to make permanent changes to your plumbing. Performance-wise, there is no difference between the top-notch models from either category.
The Filtration Process
To ensure the removal of many different types of contaminants and flawless water taste, RO systems should feature proper pre and post-filtration in addition to the RO membrane itself.
- Usually, the first filter stage in any RO system is a sediment filter. It catches rust, silt, sand, and other larger particles to improve water aesthetics but also to protect the other filter elements from clogging.
- Most of the time, the sediment filter is followed by one or two granular activated carbon or carbon block filter stages. Activated carbon is great for adsorbing chlorine and chloramine, disinfection byproducts, and all kinds of organic and chemical contaminants in general. Carbon is also the main ingredient in any water filter that helps you get rid of unpleasant tastes and odors.
- At the heart of the system lies the semipermeable membrane. It rejects almost all contaminants that are still present in the water at this point such as bacteria and viruses, cysts, salts, and metals.
- The filtered water is stored in the storage tank at this point. When you dispense water, it goes through one final carbon filter stage to remove residual taste before it comes out of the faucet.
- Filter stages that some of the more sophisticated reverse osmosis systems come with include remineralization for more natural water taste and higher alkalinity, and UV light purification which renders microorganisms harmless.
Reverse osmosis water purification in general is highly effective and removes many different types of contaminants. Still, we recommend you buy a system that’s tested or even better certified against NSF/ANSI standards. These certifications are your only guarantee that a certain model actually performs as good as claimed by its manufacturer. And apart from contaminant reduction rates for specific contaminants, NSF certifications also cover material safety and structural integrity.
When shopping, pay attention to the following standards:
- Standard 42: It tests water filters for the reduction of aesthetic, non-health-related contaminants, first and foremost chlorine. The scope of the standard also covers material safety and structural integrity of a product.
- Standard 53: Standard 53 focuses on the reduction of contaminants with health effects that are currently under regulation by the EPA. Examples are lead, chromium, and other heavy metals, asbestos ,and volatile organic compounds (VOCs). This standard also covers material safety and structural integrity.
- Standard 58: This standard is for reverse osmosis systems only. It establishes the minimum requirements for the reduction of many, many different harmful contaminants including arsenic, cadmium, chromium 3 and 6, copper, fluoride, lead, nitrate and nitrite, and radium. Material safety and structural integrity? Included!
- Standard 401: NSF/ANSI 401 addresses the ability of water treatment equipment to remove up to 15 individual contaminants which have been emerging in drinking water in recent years but are not yet regulated by the EPA. Categories include prescription drugs, over-the-counter medications, herbicides, pesticides and chemical compounds.
- Protocol P473: Perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) are man-made chemicals that up until 2000 had been widely used in the manufacturing of insecticides, electronics, paints, non-stick cooking surfaces, and other products. Exposure through drinking water may result in developmental effects to fetuses, cancer, and liver damage among other health effects. NSF Protocol P473 outlines the performance requirements for drinking water treatment units removing PFOA and PFOS.
A water purifier must be able to meet your water demand to avoid long waiting times when you are thirsty. So you either want a storage tank of appropriate size or, in case there is no tank, fast enough filtration – think booster pump. Ideally, you have both.
RO System Installation and Maintenance (Filter Replacements)
As briefly mentioned, an under sink RO system must be properly installed. Don’t worry, this isn’t overly difficult but it means drilling through your kitchen countertop or sink if you don’t have a spare hole to accommodate the water dispenser. What’s more, you need to drill a hole into the kitchen sink drain line to establish a drain connection.
If you don’t like the sound of this, consider buying a countertop filter system. This type either connects to your kitchen faucet in a matter of minutes or it’s completely standalone and doesn’t require any water connection at all.
When it comes to reverse osmosis system maintenance, how laborious and time-consuming filter and membrane replacements are is different for every model. Some filters can be replaced with a simple twist, without tools and without the need to turn off the water supply. Reverse osmosis systems that use filter housings can be slightly more difficult to service.
Incoming Water Pressure & Recovery Rates
Due to the nature of the process, any reverse osmosis filter system wastes water. And the lower the incoming water pressure, the more water will go to waste.
You can counter that using a non-electric permeate pump or an electric pressure pump. Especially the latter reduces water wastage significantly. Some RO systems come with a pump already built-in, others can be upgraded.
On a side note: The ratio of pure water to reject water is called recovery rate. A rate of 1:1 means one gallon of water is wasted for every gallon of purified water you can use. 1:2 means two gallons of water are wasted per one gallon clean water used etc. If a reverse osmosis system doesn’t feature a pump, recovery rates between 1:3 to 1:5 are the standard.
You certainly don’t need to purchase the most expensive product on the market to get purified water that’s safe and healthy. At the same time, don’t go too cheap or you might end up with substandard quality prone to causing leaks or recontaminating your water due to cheap materials used. A good price range is between $200 and $500.
Furthermore, make sure to check the price and availability of new filters and membranes. They are by far the largest expense in the long-term.
Where to Buy & Customer Service
We prefer to buy most of our water equipment online simply because you have the largest selection of products at the best prices. With point-of-use RO systems there’s no need to consult a local water expert.
What is Reverse Osmosis Exactly?
So what exactly is reverse osmosis?
Most importantly, it is one of the most widely adopted methods to filter water due to the exceptionally high purity that can be achieved. Also, reverse osmosis water filtration is cost effective which is why many bottlers around the world rely on it.
The process itself works as follows: Remember your chemistry class? Remember osmosis? Osmosis is a natural process that occurs when two salt solutions of different concentrations are separated by a semi-permeable membrane. The solvent, most of the time plain water, starts to move from the low salt solution to the high salt solution due to osmotic pressure. Only when both salt concentrations are equal and there is no more osmotic pressure does the movement of the water molecules stop.
Reverse osmosis is a little bit different. External hydraulic pressure is applied to the side of the high solute concentration. If the hydraulic pressure is high enough to overcome the osmotic pressure pointing the opposite direction, the flow of solvent can be reversed. Now the water molecules move from the high to the low salt solution. In the end, you have a highly concentrated salt solution on the one side and a very weak solution with almost no salt on the other.
In real life, the water pressure in your home’s plumbing system is the hydraulic pressure. The highly concentrated salt solution is the reject water that is flushed down the drain and the weak solution is our pure drinking water.
How Do Reverse Osmosis Systems Work?
What are the different components that can be found in a reverse osmosis water filtration system and how do they function?
RO System Components and the Multi-Stage Filter Process
The first filtration stages in a reverse osmosis system are the pre-filters. Most common are sediment pre-filters. They trap large suspended solids that might otherwise clog the other filter stage, especially the RO membrane.
Pre-filters containing activated carbon in granular or block form are great for removing chlorine and all sorts of chemicals. Both chlorine and chemicals can damage an RO membrane so it’s a good idea to have them removed before the water gets in contact with it.
Catalytic carbon blocks chlorine and chloramines.
Reverse Osmosis Membrane
The semipermeable RO membrane rejects the vast majority of contaminants that survived pre-filtration: Salts like fluoride, heavy metals including lead and chromium, radiation, microorganisms, and much more.
Two water streams leave the membrane at this point. The purified water continues its journey through the reverse osmosis filtration system. The reject water containing all removed contaminants flows down the drain.
Lastly in the filtration process come one or more post-filters. Granular carbon is used to give the water a finishing touch filtering residual contaminants.
Because output water flow is limited most RO systems come with a tank. This allows them to purify water in advance ready at your disposal. The storage tank has a pressurized water bladder inside which ensures that a sufficient amount of water flows from the dispenser.
There are two types of dispensers or faucets used with reverse osmosis systems: Standard and air-gap faucet.
If an RO water filter system uses a standard faucet with no air gap it requires at least one check valve to stop drain water from flowing back into the system causing damage.
An air-gap faucet has a, well, air gap that does exactly this: Stop water from flowing backwards into the filters – think siphon break.
Automatic Shut-Off Valve (ASO)
Due to the water bladder, a storage tank exerts increasing backpressure the more water it holds. When the tank is full and backpressure reaches a certain threshold an automatic shut-off valve closes. This stops more water from flowing into the reverse osmosis filtering system. If you draw water from the storage tank so that the backpressure drops below roughly ⅔ of the feed water pressure does the automatic shut-off valve open once more.
A check valve allows water flow in one direction only: Towards the drain. It allows reject water to pass through but blocks drain water from flowing backwards.
A flow restrictor controls the water ratio of reject to pure water and must be matched to the capacity of the RO membrane.
Electric Water Pressure Pump
An electric water pressure pump increases water pressure to force up filtration speed and improve a system’s recovery rate.
Similar to an electric pump, a permeate pump increases filtration speed and improves the permeate-to-reject water ratio.
UV light treatment is the most effective method to kill waterborne pathogens which are often found in well water. UV light inactivates bacteria, viruses, and other germs by altering their DNA.
RO purified water tends to be slightly acidic since it’s lost all mineral content. Remineralization stages are used to counter this effect. The result is more naturally tasting water that’s alkaline.
Reverse Osmosis Filtration System Recovery Rates
All reverse osmosis systems waste water. There is nothing you can do about this. The reject water that flushes down the drain contains all the contaminants that couldn’t make it past the RO membrane.
That said, different RO water filter systems have different recovery rates, meaning the amount of water that can’t be used varies from model to model. The best systems with a built-in pump waste no more than 20 percent (80% recovery rate). For comparison, the most affordable of-the-shelf units waste around 5 gallons for every gallon of filtered water produced (16.7% recovery rate). By the way, the ideal water pressure for most RO systems is somewhere around 60 psi. Low water pressure of less than 30 to 40 psi is usually insufficient.
The ratio of pure water to contaminated water is not only a function of incoming water pressure. Other parameters are water temperature, solute concentration, and membrane pore size which you cannot influence.
What Do Reverse Osmosis Filters Remove from Water?
What do RO systems remove from water? That’s a long list! Some manufacturers speak of more than 1,000 potential pollutants including:
- Chlorine and chloramine
- Disinfection byproducts
- Nitrate and nitrite
- PFOA and PFOS
- Different types of metals, most importantly heavy metals
- Microorganisms like bacteria, viruses, and cyst
- Other chemicals and organics
What Does TDS Mean?
TDS is an abbreviation and stands for total dissolved solids. It measures the combined total of dissolved organic and inorganic impurities in water in parts per million.
Is a Reverse Osmosis System Worth It? – Advantages & Disadvantages
Reverse osmosis water systems have advantages and disadvantages.
- The number one advantage is that with relatively little effort can you reduce or entirely remove certain contaminants from water that other filtration or purification methods wouldn’t even touch. What comes to mind is hexavalent chromium, a cancer-causing chemical found in all 50 states of the U.S. In a nutshell, RO filters produce highly pure, healthy water.
- Another benefit of using a reverse osmosis water filtration system is improved water aesthetics: Chances are that the purified water will taste and smell a whole lot better.
- Generally speaking, filtering your own tap or well water saves you a lot of money if bottled water is the only alternative.
- Also, RO water filters are easy to install and maintain. This applies even more to counter top reverse osmosis systems.
- One of the biggest downsides of reverse osmosis is the fact that some proportion of the water goes to waste.
- Furthermore, the reverse osmosis process is so effective that even beneficial minerals are removed from water.
- Compared to other water filtration systems, RO units are rather expensive.
Does Drinking RO Water Pose a Health Risk?
RO water purification removes close to 100 percent of impurities from water which is great. However, this also includes healthy minerals especially calcium and magnesium.
On the one hand, those minerals can’t add to your recommended daily intake anymore. Around 80 percent of our daily calcium and magnesium intake comes from food, the rest from drinking water. This is why it makes sense to supplement with calcium + magnesium or mix them back into the water before consumption. For the majority of other elements drinking water provides less than 5 % of total intake, so no reason to worry about them.
Another frequently mentioned problem with purified water lacking minerals is acidity. Research suggests that slightly acidic water is not a health issue, though. You just need to make sure that it’s stored in a container that doesn’t corrode.
Remineralizing RO Purified Water
The easiest way to make sure that you get those minerals in which were lost during the filtration process is by means of a remineralization filter. A remineralization filter is simply an extra stage that you can add to your reverse osmosis filter system. The healthy minerals will leach into the water over time.
Of course, you can also remineralize your RO purified water manually by mixing in an electrolyte blend. Green powder blends and mineral-rich salts work, as well.
Do I Even Need a Reverse Osmosis System?
Do I even need a reverse osmosis system, is a question that gets asked repeatedly. The only way you can know for sure is having your water tested. Maybe your tap or well water doesn’t require any additional treatment at all; but chances are small. Most waters need some sort of purification for health reasons or to improve the taste of the water – and smell! And some waters need reverse osmosis filtration in particular because it’s the only method that’s effective against certain types of contamination.
So, the first step is finding out more about your water. Which contaminants are present and at what concentrations? What’s the hard water and TDS level?
If you are on city water you can check the latest water quality report provided by your local utility. Alternatively, visit https://www.ewg.org/tapwater/, enter your ZIP code, and choose your utility from the list. The EWG Tap Water Database lists all detected contaminants. The only issue with this approach is that water utilities aren’t required to test for all potential pollutants but a limited selection.
This is why you should think about paying an independent lab to do your own testing. If you have your own private well this is your only option anyway. Tip: Check out Tap Score. They are a reliable partner of ours.
How to Install an Under Sink RO System
Installing an RO water filter system isn’t difficult. Countertop units are installation-free and can be attached to faucets in no time. Under sink filter setup takes longer but isn’t too complicated either. Here is a basic outline of the installation process. Just keep in mind that your system may require a different approach so make sure to follow the manufacturer instructions precisely.
Tip: There are dozens of helpful tutorial videos published on YouTube. They might be worth checking out if you’re stuck and don’t know how to proceed.
Tools and Supplies
Here is a list of tools and supplies you’ll need in addition to all the different components that already come with your RO system itself:
- Utility knife
- Adjustable wrench
- Power drill
- Drill bit, size depends on faucet stem diameter
- Phillips head screwdriver
- Large bucket and towel
Location, Location, Location
If you don’t have a whole lot of free space in your sink cabinet you can also do the installation in your utility room, basement, or garage and run a water line to the kitchen. However, you must not install a reverse osmosis system where freezing temperatures occur.
Step-by-Step Installation Instructions
1. The Water Dispenser
Start the installation by drilling a hole in your countertop or sink to accommodate the water faucet. Think about where you want to position it carefully, then mark the spot with a center punch.
For the drilling, you may need to make a pilot hole first. Before installing the faucet, clean up any sharp edges. Insert the faucet stem through the hole and secure it with a hex nut.
2. The Drain Connection
To establish a drain connection you also need to drill a hole into your sink drain line. Choose a spot as far away as possible from the garbage disposal and dishwasher discharge. Most manufacturers recommend going at least 6 inches above the p-trap. Also, never drill a hole in the bottom of the drain water line to avoid clogging. The top or the side is fine.
Most drain adapters use two clamps with can be screwed together. Align the hole of the drain saddle with the newly drilled hole in the drain water line before tightening.
3. The Feed Water Adapter
The feed water adapter or feed valve connects an RO system to the cold water supply.
Before you proceed, turn off the cold water and flush as much of the remaining water as possible by opening your kitchen faucet. With a bucket at the ready, remove the tubing from the cold water valve. Install the feed water adapter. Connect the cold water tubing of the faucet to the new adapter and turn the water back on.
4. The Storage Tank
Put the water storage tank in place. Both upright and horizontal position is possible. Before installing the tank valve, wrap enough plumbers’ tape around the threaded port.
5. The Module
With standard RO system modules mounting is optional. Use the color-coded tubing to establish the different connections: To the tank, to the faucet, to the feed water valve, and possible to any inline filters.
More or less all reverse osmosis systems use quick-connect fittings. To make a connection, push the tubing in as far as possible.
6. The Filter Elements
Attention: Wash your hands before proceeding.
Often, the filters and membrane are already inserted in the respective housings, but are still wrapped in plastic which needs to be removed. Unscrew each filter housing one after another, unwrap the filter cartridge inside, put it into its housing, and screw the housing back on. Tighten with the provided filter wrench.
For the RO membrane, unscrew the membrane housing cap, unwrap the membrane and push it into the housing socket. Screw the cap on and tighten.
Now your new reverse osmosis filter is ready to go to work. Open the feed valve and the water dispenser. Check for leaks. Note: It can take several minutes before water reaches the RO faucet.
Lastly, close the dispenser and open the valve on the water tank. Let it fill completely before you drain the entire tank. Repeat the process and flush a second time.
Reverse Osmosis System Maintenance
RO system maintenance involves two tasks:
- Replacing the filters in a timely manner. Most last between 6 and 12 months. RO membranes usually last 2 or 3 years.
- Clean and possibly sanitizing the filter housings and storage tank.
Every 6 to 12 months, depending on the cartridges themselves, your water usage, and water quality, filters require replacement. You need to remove the old filter cartridges and insert new ones. Here’s how:
- Shut off the cold water source as well as the RO storage tank valve.
- Depressurize the system by opening the RO faucet.
- Unscrew one filter housing.
- Take out and discard the old filter cartridge.
- Insert a new filter.
- Screw the filter housing back on and tighten with the filter wrench.
- Repeat steps 3 to 6 for each filter stage.
- Turn the water source and tank valve back on.
- Flush the new filters as instructed by the manufacturer. Meanwhile, check for leaks.
Changing the RO Membrane
Depending on the type and quality of membrane, your daily water usage, and the condition of the incoming water, reverse osmosis membrane filters need replacing every 2 to 3 years. Simply follow the above steps when it’s time to replace yours.
Measuring the Current Membrane State
You can measure the current state of your membrane using a TDS meter. First, measure and take note of the total dissolved solids of the feed water. Do the same for the filtered water. Then you can calculate the total dissolved solids rejection rate a.k.a. remaining effectiveness of your membrane using this formula:
Rejection in % = (Feed Water TDS – Filtered Water TDS) / Feed Water TDS x 100
A membrane in perfect condition removes up to 99 percent TDS.
Cleaning and Sanitizing
Once a year, you want to thoroughly clean and maybe even sanitize your RO water filter system to avoid germs from accumulating.
- First, make sure to shut off the water source as well as the RO storage tank valve.
- Remove all filters elements from their housings.
- Clean the inside of the filter and membrane housings with dishwater. Thoroughly rinse afterwards.
- If you also want to sanitize your RO system, you can do so using regular bleach. Add a small cup of bleach into the first filter housing and screw all empty housings back on. Open the valves and let the storage tank fill. Flush all water. Let the tank refill one more time and flush again. Remove all housings.
- Screw the housings back on with new filters and membrane inside.
- Open the water source and tank valve.
- Flush the new filters as instructed by the manufacturer. Meanwhile, check for leaks.
Frequently Asked Questions (FAQ)
Which is better distilled or RO water?
Both are highly pure, but we prefer remineralized RO water.
Is drinking reverse osmosis (RO) water bad for you?
It is not. And if you are worried about not meeting your daily required intake for magnesium and calcium, you can simply use a remineralization filter or electrolyte blend.
Does reverse osmosis kill bacteria?
Reverse osmosis does not kill bacteria, but it rejects it nevertheless.
How pure is reverse osmosis water?
Water purified with a conventional reverse osmosis water filtration system for home use is up to 99 percent pure.
How much does a reverse osmosis system cost?
Cheaper systems usually cost little more than $100. However, their quality is often substandard which might cause leaking among other issues. We recommend investing at least $200 in a more high quality water filter model. Keep in mind, anything above $500 is overpriced unless you get a lot of useful extras like remineralization and UV filter treatment.
Is reverse osmosis the same as distilled water?
No, distilled water is the end product of water distillation.
Why does my RO water smell?
It’s quite possible that your RO system has accumulated mold or algae over the years. Cleaning could solve the problem. If that doesn’t help you may need to replace the entire unit.
An RO filtration system can make a great addition to your home. You just need to buy one suited for your water conditions. Our first choice is the AquaTru. If you prefer under sink RO systems go with the Aquasana OptimH2O. The Waterdrop WD-G3-W is a great tankless model. For well water filtration we recommend the Home Master TMHP HydroPerfection. And lastly, the Crystal Quest Thunder is our #1 portable unit.
Questions about our reverse osmosis system reviews or other brands like APEC Water Systems or Express Water? Leave a comment below!
- 5 Best Countertop Reverse Osmosis System Reviews (+ Portable)
- Water Masterz Best Whole House Water Filtration System Review Guide
- The Best Water Filter for Lead Removal? 10 Reviews + Guide 2021
- Guide: How to Filter Lead Out of Water
- Fluoride Filter Buying Guide by Water Masterz
-  https://www.lenntech.com/library/fine/absolute/absolute-nominal-filters.htm
-  https://www.nsf.org/knowledge-library/perfluorooctanoic-acid-and-perfluorooctanesulfonic-acid-in-drinking-water
-  https://www.ewg.org/tapwater/reviewed-chromium-6.php
-  https://www.who.int/water_sanitation_health/dwq/nutrientsindw.pdf
-  https://www.healthline.com/nutrition/acidic-water
Jason is the founder of Water Masterz and head of content creation. After six years in the industry, he has tremendous knowledge and first-hand experience on all things related to water treatment.
His credo: Not a single American should have to drink unhealthy water at home.