You are probably here because you want safe, healthy drinking water for you and your family or want to learn about water filtration systems. A home water filtration system can improve overall water quality throughout your house by removing contaminants, bacteria, and biofilms from your entire plumbing system.
Unfortunately, no tap water is safe anymore, even if you have “high quality” city or well water. Plus, there are no guarantees that bottled water is any better than your tap. Reverse osmosis (RO) systems filter water through a semi-permeable membrane that blocks contaminants such as lead, chlorine, and fluoride, making them an effective solution for safer drinking water and providing great tasting water for drinking and cooking.
RO-System.org is your reliable source for the best reverse osmosis system reviews and detailed information about all water filtration systems. Our experts test and rank the options so you don’t have to!
Our rankings are based on hands-on testing, features, price, total cost of ownership, warranty, and customer reviews.
Table of Contents
- Our Top Picks
- Top Reverse Osmosis Systems
- 1. Waterdrop X Series X12 Reverse Osmosis System
- 2. Home Master TMHP HydroPerfection Reverse Osmosis System
- 3. NU Aqua Tankless Reverse Osmosis System
- 4. Waterdrop G3 P800 Reverse Osmosis System
- 5. Frizzlife PD600-TAM3 with Alkaline Remineralization
- 6. Home Master TMAFC-ERP Artesian Reverse Osmosis System
- 7. NU Aqua 7 Stage Reverse Osmosis System
- Compare the Top RO Systems
- Why Do You Need a Water Filter?
- Reverse Osmosis System Buying Guide
- Installation and Maintenance of RO Systems
- Environmental Impact and Sustainability
- Need More Info?
Our Top Picks
#1 Overall: Waterdrop X Series X12
The smartest faucet, an integrated TDS meter, a UV filter, remineralization, and both the highest daily output and most efficient waste water ratio make this system the top choice!
Overview | Full Review
Runner Up: Home Master TMHP HydroPerfection RO System
With nearly every filter including ultraviolet, this system is the ideal option to power your refrigerator ice maker and can be easily customized.
Overview | Full Review
Best Mid-Range: NU Aqua Tankless 600 RO System
This tankless RO system is super-efficient and comes with a smart faucet, remineralization filter, and 120 day home trial guarantee.
Overview | Full Review
Best Budget: NU Aqua 7 Stage RO System
This affordable reverse osmosis water filter has lots of features including UV and remineralization at a great price.
Overview | Full Review
Top Reverse Osmosis Systems
Our top rated RO water filtration systems are “point-of-use” under sink systems, specifically under sink filters, that are installed and used at a single location, which is usually under the kitchen sink. Under sink installation may require some DIY skills, such as drilling into countertops and connecting plumbing, and you should consider the available cabinet space before installation.
These reverse osmosis water purification systems include a dedicated faucet that is installed alongside your standard tap water faucet to produce filtered water just for drinking and cooking. With additional parts, you can also run a pure drinking water line to your refrigerator, if it is has a water dispenser and/or ice maker. Routine filter change is essential for maintaining water quality and system performance.
Compared to other filter methods like pitcher filters or faucet filters, under sink systems with reverse osmosis technology can remove other contaminants that these alternatives may miss. Conducting a water test can help determine which system is best for your needs by identifying specific contaminants in your water supply.
If you want to learn more about the newer tankless style options we recommend, check out our review of the top tankless reverse osmosis systems.
1. Waterdrop X Series X12 Reverse Osmosis System
The Waterdrop X Series represents a significant advancement in under-sink systems, offering a compact and efficient solution for water purification.
With its efficient filtration process and 11 stages, it ensures clean, mineral-infused drinking water while minimizing waste. Advanced, user-friendly features make it easy to use and maintain.
High-Volume Filtration:
The Waterdrop X12 RO system delivers up to 1200 gallons of purified water daily, with a waste-to-pure water ratio of 3:1, and a fast flow rate of 3.75 seconds for a cup of pure water, outperforming many other systems in speed and convenience. Its filtration performance is driven by high-quality RO filters, which are designed for superior contaminant reduction, ensuring the removal of a wide range of impurities and meeting rigorous certification standards.
Tankless reverse osmosis systems provide continuous flow and save space compared to traditional tank systems.
Health Benefits
The multi-stage filtration process ensures contaminant reduction including bacteria, while the remineralization stage adds beneficial minerals back into the water.
Ease of Use
The system is user-friendly, featuring a smart faucet with real-time TDS monitoring and simple filter replacement, making maintenance hassle-free.
Learn more in our review of the Waterdrop X Series X12 or click the button below to visit the manufacturer’s website.
Waterdrop Filters on Sale!
2. Home Master TMHP HydroPerfection Reverse Osmosis System
If you don’t to want waste time comparing options and just want to be sure you are covered in every situation, then the Home Master TMHP HydroPerfection is the perfect filtration system for you. It comes complete with every major feature and every possible filter – 9 stages in all! The system uses a variety of filter types, including sediment, carbon, remineralization, and UV filters, which work together to target a broad range of contaminants for comprehensive water purification.
Permeate pump
The Home Master TMHP includes a permeate pump, which increases the output of the system to 75 gallons per day and reduces the amount of waste water needed to flush the RO membrane to just 1 gallon for every gallon of purified drinking water produced.
Remineralization stage
It has a remineralization filter that adds safe calcium and magnesium minerals back into the RO water and raises the pH to be more alkaline. This creates a fresher tasting water that compares to good bottled water.
UV filter
The system also has a UV (ultraviolet) light that will kill 99.8% of microorganisms that may contaminate your water. Municipal water sources are usually low in microorganisms but well water and other natural sources can have higher levels.
In addition, Home Master comes with a 5-year warranty! When considering the operating cost, keep in mind the expenses for filter replacements and routine maintenance, which are important for long-term value.
For more details on this system, check out our full Home Master TMHP HydroPerfection reverse osmosis review or click the button below.
Customize your faucet, tank, and upgrades!
3. NU Aqua Tankless Reverse Osmosis System
NU Aqua Systems has joined the tankless trend and added the NU Aqua 600GPD Tankless reverse osmosis water filtration system (WU-600GPD-TL) to its already impressive lineup.
What sets this system apart?
It is tankless
It has an integrated pump and is not slowed down by a water tank so it can process up to 600GPD faster than a conventional under sink system. Unlike some systems that suffer from slower flow rates, especially when filling larger containers, the NU Aqua delivers a consistently strong flow without sacrificing filtration quality.
It is super-efficient
There is a 2:1 ratio of pure water to waste compared to other RO systems that only get 1:1 and many that get 1:2 or 1:3… The design also helps reduce overall water consumption compared to traditional RO systems, making it more eco-friendly and cost-effective.
Smart and compact
The RO faucet has an LED ring that glows blue to let you know everything is working normally or red to let you know that one of your filters needs to be replaced. The system body also has lights to show filter status and overall system health.
This is also one of the most compact systems you can put under your sink and is easy to install.
Lab data supports the NU Aqua’s performance claims and contaminant removal efficiency, providing confidence in its filtration capabilities.
For more details on this system, check out our full NU Aqua Tankless 600GPD Reverse Osmosis Review or click the button below.
NU Aqua Sale!
4. Waterdrop G3 P800 Reverse Osmosis System
The Waterdrop G3 P800 is an evolutionary upgrade to the very popular Waterdrop G3 (P400) and offers an array of features that are not available in any other tankless under-sink RO systems.
Fast output
This system can produce a whopping 800 gallons of filtered water per day (GPD), which is enough for a very busy household and even small businesses that requires large amounts of filtered water.
Efficient processing
In addition, it does this with an exceptional 3:1 waste water ratio, meaning it creates only 1 gallon of waste water for every 3 gallons of pure water.
Extra features
This system comes with an integrated UV filtration stage that effectively removes any microorganisms that may still be present in the water and a built-in TDS (total dissolved solids) meter in the smart faucet to report the quality of the filtered water.
The Waterdrop G3P800 is NSF certified for its contaminant removal performance, including its ability to remove chlorine and lead.
For more details on this system, check out our hands-on Waterdrop G3 P800 reverse osmosis review or click the button below.
Waterdrop Filters on Sale!
5. Frizzlife PD600-TAM3 with Alkaline Remineralization
The Frizzlife PD-600-TAM3 makes it near the top of the list of reverse osmosis water filtration systems because of its excellent features and competitive price tag.
What makes it so good?
Remineralization
The Frizzlife system comes with an alkaline remineralization filter that adds essential minerals back to the filtered water and raises the pH to more than 7.5.
Filtration of health-related contaminants
This system is highly effective at removing health-related contaminants such as lead and disinfection byproducts, helping to ensure safer and cleaner drinking water for your household.
Smart features
Only one other system on our list has an integrated digital TDS meter built into the system like this Frizzlife. This very helpful feature continuously tests and reports on the quality of your water after it has been filtered.
Tankless design
With the fastest 600 GPD RO membrane and an internal booster pump, this system has high throughput and is very efficient.
Combine all of the features above with the smaller size and easy maintenance of the tankless design and you have a system that is sure to provide great water in a great package.
For more details on this system, check out our full review of the Frizzlife PD600 or click the button below.
Frizzlife Sale!
6. Home Master TMAFC-ERP Artesian Reverse Osmosis System
The Home Master TMAFC-ERP water filtration system combines the perfect balance of useful benefits, popular features, and value in one package.
There are two big features that set the TMAFC-ERP apart from other mid-range options and makes it one of the top clean water systems…
Remineralization stages
Water passes through a remineralization filter TWICE (a unique feature of the Home Master). This adds safe minerals back into the RO water and raises the pH to be more alkaline. The result is a fresher tasting mineral water that many people prefer.
Permeate pump
In addition, it comes standard with a permeate pump, which is a non-electric device that increases the water pressure before it enters the reverse osmosis membrane. This reduces water waste up to 80 percent and increases water production up to 50 percent.
Nice design features
The included “Fast Flow RO kit” uses larger fittings and tubing to speed up the fill rate at the faucet so you get water as fast as possible. Home Master makes high quality filters that are modular in design and built for easy filter changes without any tools.
Also, Home Master has an excellent 5-year warranty, which is better than most of the other top companies in our list.
For even more details on this system, check out our full Home Master TMAFC-ERP Artesian reverse osmosis review.
Customize your faucet, tank, and upgrades!
7. NU Aqua 7 Stage Reverse Osmosis System
The NU Aqua 7 Stage Reverse Osmosis Water Filtration System has all of the same features as many competitors but at a much lower price.
Many stages
In addition to having the 5 basic stages of filtration, this system also offers:
- UV (Ultraviolet light) Filter to destroy bacteria and other microorganisms in well water
- Alkaline Filter to add beneficial minerals back to the RO water
- Booster Pump to improve efficiency and decrease wastewater
Better taste for beverages
Filtered water from this system can noticeably improve the taste of your morning coffee, tea, and other beverages, making your daily drinks more enjoyable.
Extra features
The other big feature is a 5 year manufacturer warranty and lifetime support. Only one other brand in our recommendations offers a 5 year warranty and it’s a great benefit.
Finally, NU Aqua provides a free digital PPM meter water tester so that you can get a quick measurement of overall water quality. This is a nice bonus to round out the package.
For more details on this system, check out our full NU Aqua Systems Reverse Osmosis Review or click the button below.
On Sale Now!
NU Aqua Sale!
Compare the Top RO Systems
The cost of reverse osmosis systems can vary significantly based on features, installation complexity, and maintenance needs.
Why Do You Need a Water Filter?
According to the Environmental Working Group’s (EWG) Tap Water Database:
- 81% of American’s water contains contaminants linked to cancer
- 77% of Americans are drinking hexavalent chromium (the “Erin Brockovich” chemical)
- Water samples from all 50 states have been found to contain: arsenic, chromium-6, disinfection byproducts, lead, nitrates from fertilizers, and radiological contaminates.
These water contaminants include a wide range of harmful substances such as heavy metals, chemicals, and invisible toxins. Effective contaminant reduction and contaminant removal are key goals of advanced water filtration solutions, ensuring your drinking water is safe.
Reverse osmosis systems can improve the taste and odor of water by removing chlorine and other chemicals used in municipal water treatment.
Also, the EWG recommends reverse osmosis water filters as the “most effective” way to filter your drinking water since it will remove up to 99% of common and dangerous contaminants. There are various water filtration solutions available, but reverse osmosis is among the most effective for thorough contaminant removal.
But picking the right options for your first water filtration system can be overwhelming if you don’t know much about water treatment.
If you decide that a RO drinking water filter system is not right for you, check out our whole house water filter reviews for some great alternatives.
Before you start looking the best water purifier for your home, check out our Reverse Osmosis Buying Guide (below). You will learn how the process works, the terms that you will come across in your research, and understand which features matter for your health.
Reverse Osmosis System Buying Guide
Access to clean, healthy water is important for all living things and there are plenty of people through the ages that agree.
Our team has tested dozens of water filtration systems over the years to provide you with reliable recommendations. Here is important information you can use to decide on the right water filter for you. Be sure to consult the user manual for each system, as it offers essential guidance for installation and maintenance.
What is Reverse Osmosis?
Reverse Osmosis (also referred to as “RO”) is a process where you remove impurities from water by pushing it through a permeable membrane. This is known as the RO process, a critical step in the overall water treatment process. The RO process involves forcing water through a semi-permeable membrane, which blocks contaminants and allows only clean water to pass through, resulting in highly purified drinking water.
It is the opposite of osmosis, which is one of the most important processes in nature. In osmosis, water that is more pure naturally flows towards water that is less pure even if it has to pass through a membrane. Reverse osmosis uses pressure to force less pure water through a membrane that blocks impurities so that you end up with very pure water on the other side.
Here is an informational resource that explains reverse osmosis in greater detail and the US Centers for Disease Control and Prevention (CDC) has prepared a fact sheet about the effectiveness of different water filtration systems for purifying water.
What Does a RO Filtration System Remove?
Reverse osmosis water systems are specifically designed to reduce contaminants, including a wide range of water contaminants and health related contaminants that may be present in your tap water.
Only a RO water system can remove or drastically reduce all of the following harmful contaminants:
- Aluminum
- Ammonium
- Arsenic 5
- Bacteria
- Barium
- Cadmium
- Calcium
- Chloride
- Chlorine
- Chloramines
- Chromate
- Chromium
- Copper
- Cynanide
- Cysts
- Flouride
- Iron
- Lead
- Magnesium
- Manganese
- Mercury
- Nitrate
- Nitrite
- Pesticides
- Phosphate
- Potassium
- Protozoa such as Cryptosporidium and Giardia
- Radium
- Radon
- Selenium
- Silver
- Sodium
- Strontium
- Sulfate
- Sulfite
- Turbidity
- Viruses
- Zinc
- And many more!
Reverse osmosis can help eliminate contaminants that are tasteless and odorless, such as radon, which can be present in well water.
How Does Reverse Osmosis Work?
Although all the systems that we have reviewed are referred to as “reverse osmosis systems,” the RO filter is only one stage of the whole water treatment system. The RO membrane is just a very fine filter.
The actual setup varies slightly from one machine to the next and between manufacturers but the layout is basically the same as shown in the image above.
Water passes through a pre-filter (1), which removes dirt and sediment from the water, protecting the RO membrane. Next, the water flows through a carbon block filter, which targets contaminants like chlorine, lead, VOCs, and heavy metals. Then, the RO filter (2) or RO membrane filters out most minerals, contaminants, or particles in the water, which are then flushed down the drain. Finally, the water passes through one or more post-filters (3 and 4), often carbon block filters, that provide a final polish to the taste of the water before it is dispensed by removing off-tastes or gasses that affect the odor of the water.
While some RO systems will have additional components such as UV lights, permeate pumps to increase the line pressure of the in-flowing water, and remineralization functions, the main process does not vary much.
Pre-Membrane Filters
In unfiltered drinking water, there are materials that, although invisible to the naked eye, are large enough to damage the reverse osmosis membrane. Typically, this sediment filter (or filters) will remove all solids such as rust and sand, chlorine, etc. with a 5-micron filter at the start of the filtration process.
RO Membrane
The RO membrane (also known as reverse osmosis filter) is an ultra-fine filter that removes everything larger than 0.001 microns. This means that virtually the only thing that can pass through the permeable membrane is pure water.
These filters remove up to 99 percent of dissolved solids from the water. With the pores of this RO membrane being so fine, it is understandable that water pressure would affect how quickly the water could pass through. Higher feed pressure is ideal for efficient reverse osmosis water filtering.
Post Filters
Most RO systems pass water through an additional carbon filter at the final stage to remove any lingering tastes and odors from the purified water. The purified water is then delivered to a storage tank at the end of the filtration process until required. There can be other stages that are considered a post filter as well.
Hard Water
Reverse osmosis machines do remove minerals from purified water but is not meant to replace a water softener if you have hard water.
Water softeners work specifically to remove the “hard” minerals of calcium and magnesium from water and make it “soft.” Hard water is not unhealthy but can cause many problems for your appliances, plumbing, and for the people that bathe in it. Be sure to check out our reviews of water softeners to find out more.
85% of U.S. households have hard water and installing a water softener will both improve the water at all points of use and protect residential systems from dealing with hard water.
Optional Accessories
Be sure to check out our guide to the most popular water filter accessories for even more options. This can include refrigerator connection kits, alternative faucets and water tank sizes, [pitcher filters] as an alternative or supplementary water filtration accessory, as well as water quality testing tools.
Remineralization
Some reverse osmosis systems include additional features like remineralization filters to improve water taste and quality.
Standard on some systems or available as an optional extra, a remineralization stage adds beneficial minerals such as calcium and magnesium, and sometimes potassium back to the reverse osmosis water. Not only does this enhance the taste of drinking water but it also raises its pH value by making it less acidic and more alkaline.
Permeate Pump
If you have low water pressure or even just want to increase the output of your RO filter system and waste less water, you should add a pump. It is possible to buy an electric pump but a permeate pump is recommended and is included as standard on some of our recommended systems, such the Home Master TMHP.
A permeate pump is a clever non-electric device that circulates the water to increase the feed pressure entering the system. Not only does this improve the amount of water output by the system by 50% it also greatly reduces the water needed to flush the reverse osmosis membrane. Instead of using 4 gallons of wastewater to produce a gallon of purified water, systems with a permeate pump waste 1 gallon to produce a gallon of purified reverse osmosis drinking water. You can add a permeate pump to any system after installation.
Some systems contain a powered booster pump that will ensure proper water pressure inside of the RO system for optimal efficiency.
UV Light
A few of our top undersink RO systems come with an Ultraviolet (UV) light, although more should include one.
The purpose of the UV light is to kill 99.9% of all microorganisms that may be in the water including bacteria and viruses. The RO filter often blocks most microorganisms before they can reach the UV filter, but you want to be sure if you have well water or a questionable water source.
Municipal (city) water is often treated to kill microorganisms already although old or dirty pipes can still re-introduce more. Well water and other natural sources can contain a much higher level of microorganisms and a UV filter is recommended if your water could be contaminated. Testing your water is the only way to know for sure and you can add a UV light to any system after installation.
Keep in mind that you will need an outlet near the RO system so you can plug in the UV light.
Reverse Osmosis Terms
When learning about reverse osmosis filtration systems, there are various terms that manufacturers use that may be new to you. Here are a few of the more common terms and what they may mean.
Filter types: This refers to the different kinds of filters that can be used within a reverse osmosis system. Some systems are compatible with a variety of filters, allowing you to choose from different brands or filtration options for customization and potential cost savings.
Replacement filters: This term describes the process of replacing used filters with new ones. Regularly installing replacement filters is essential for maintaining effective filtration and ensuring the system continues to provide high-quality water. Replacement filters are an ongoing operating cost, but are required to maintain the water quality of a home water filtration system and ensure maximum contaminant reduction.
Filter life ranges from 6 to 24 months depending on the manufacturer, the type of filter, and the contaminant removal needed in your situation. Filter performance will be lower if you don’t keep track of filter life and perform regular water tests.
Stages
Every RO system has a distinct number of stages that water will pass through in the filtration process. Each stage performs a different function to either filter or process the water in some way. The number of stages is not the only way to compare how good systems are but more stages usually means more is done to purify and guarantee high quality water.
4-5 stages are standard in most reverse osmosis systems. Many of our recommended options have even more stages!
Storage Tank
All of our top rated systems that install under the sink come with a pressurized storage tank that will hold the purified reverse osmosis water. By pre-filtering enough purified water to fill the tank, the system ensures that you will get a quick response from your filtered water faucet.
Without the storage tank, you can only have filtered water as fast as the system can produce it in real time. You can replace the standard tank with a larger one if you often need more pure water on demand or higher tank pressure.. Alternatively, you can look at one of the tankless reverse osmosis systems that don’t use a tank and produce reverse osmosis water faster.
Water Output
A measure of how much water a system can typically process in a day is often referred to as the system’s ‘flow rate.’ Flow rate is a key performance metric that indicates the speed at which purified water is delivered, usually measured in gallons per minute (GPM) or gallons per day (GPD). A higher flow rate means more water is available in less time, which directly impacts user convenience, especially when multiple people or appliances rely on the system.
The daily water production capacity for under-sink systems typically ranges from 50 to 100 GPD for singles/couples and 400-800 GPD for families.
All RO systems that we have reviewed use the same standard test for documenting their gallons per day (GPD) output figures. These tests are based on the water coming in at 77 degrees Fahrenheit (25 Celsius) and with a water pressure of 60 psi.
The truth is that in real life installations, very few places have these ideal conditions. This means that quite often the output from a RO system is less (in some cases considerably less) than suggested in the datasheet. It is quite complicated to calculate the exact figures that you can expect to get from any system since lower pressure, lower temperature, and high TDS levels also lead to a reduction in flow rate and overall output.
Waste Water
One of the common complaints about RO systems is that they waste a great deal of water when flushing the RO membrane. Reverse osmosis systems produce wastewater during the filtration process, which can vary by model.
With undersink RO systems, the range is 0.5-4 gallons of water being wasted to produce a gallon of purified water. The amount of water used is highly dependent on the pressure of the inflowing water – higher pressure means less water is needed to flush the reverse osmosis filters.
The average across the systems we reviewed is about 2 gallons wasted per 1 gallon filtered. A permeate pump reduces the water waste to 1 gallon for every gallon of filtered reverse osmosis water produced and a powered pump can lower waste water to 0.5 gallons. The waste water ratio directly impacts overall water consumption, so choosing a more efficient RO system can significantly reduce your household’s waste water compared to less efficient models.
If waste water is a concern, make sure to look for a system with a lower waste to filtered water ratio. If you want to reclaim the “wasted” water, the waste pipe from the system can be fed into the normal cold faucet or even diverted for watering the garden.
pH / Acidic / Alkaline
The pH refers to how acidic (low pH) or alkaline (high pH) the water is.
The RO systems that we have reviewed accept a wide range of pH values in the feed water. Manufacturers that comply with EPA Drinking Water Standards will accept water that has a pH value of between 6.5 and 8.5. Water that passes through RO systems tends to have the pH value lowered when the healthy minerals are filtered out with everything else. This lower pH makes the purified water slightly more acidic, which can taste bland to some people.
If this is a problem for you, you may want to look at systems that remineralize your drinking water. A remineralization stage increases the pH value to a level closer to neutral and creates a taste that is similar to good bottled water.
TDS
TDS stands for “total dissolved solids.” These usually include inorganic salts such as calcium, magnesium, potassium, sodium, bicarbonates, chlorides, and sulfates, along with some small volumes of organic matter that are dissolved in water. The EPA sets a maximum TDS level of 500mg/L in drinking water is its Secondary Drinking Water Standards.
There are two ways that the total dissolved solids can be measured. The first way is in a lab under stringent controlled conditions, which is expensive and time consuming. Lab data is used to verify TDS reduction and system performance, ensuring that the best reverse osmosis system meets certification standards. The second is by measuring electrical conductivity. Although this method is not as accurate as the lab test, the results gained by a fairly inexpensive meter are within 10% of the lab results. An RO system that is functioning well should reduce TDS in filtered water by about 90% – but this is variable.
Simple water test tools can show you your unfiltered tap TDS compared to your filtration performance.
The ideal way to know if the filters in your RO systems are due for replacement is to measure both the pre-filtered and post-filtered reverse osmosis water to compare the TDS values.
Air Gap Faucet
What is an air gap faucet? The air gap provides a siphon break for under sink RO systems. This means that if the sink should get backed up, there is no way that the dirty water can be siphoned back into your RO system. In some localities, it is part of the plumbing code that all RO systems should have an air gap faucet, but it is rare.
A few RO systems come with an air gap faucet, although most offer only a standard faucet. You can always upgrade your faucet in any system if you prefer or local plumbing code requires it.
While there are advantages to air gap faucets, a standard faucet is usually preferred. This is because air gap faucets are more complicated to install and usually need a larger, non-standard counter hole. Air gap faucets need three pipes to connect instead of just one and, in some cases, they can be noisy.
Whole House Reverse Osmosis Water Filter Systems
The under sink RO water filter systems listed above are point-of-use and will only provide filtered water at the location they are installed.
If you decide you want clean water throughout your entire house, or you have very high water volume needs, then a whole house reverse osmosis system would be the most complete home water filtration system for your home or business, providing purified water to every tap and appliance.
With a whole house RO water system, you get the same excellent water filtering benefits as the systems described on this page, but at every sink, shower, and appliance in your house. These systems use a multi-stage water treatment process, typically involving reverse osmosis, which forces water through a semi-permeable membrane to remove contaminants and deliver nearly pure water across your entire plumbing system.
Whole house RO is not without its disadvantages, but you can learn more in our whole house RO review and guide.
There is also the option to install whole house water filters without reverse osmosis that will do a great job of removing common contaminants from city water or well water.
Installation and Maintenance of RO Systems
All of the top reverse osmosis systems that we have reviewed here require some degree of installation before they will operate.
Reverse osmosis water filtration systems are designed for installation under a sink, with connections into the cold water feed pipes and waste pipes under a sink. While installation for many of these systems can be a “do it yourself” project for those with basic DIY skills and tools, the process can vary in complexity. Some systems may require professional installation, especially if the setup involves more advanced plumbing or drilling into countertops for the filtered water faucet. Always consult the user manual for detailed installation and maintenance instructions.
Routine maintenance, such as changing filters, is essential to ensure effective filtration and optimal system performance. The system manual will also provide guidance on the recommended schedule and steps for changing out the filters.
However, if these systems require too much installation or don’t work for your situation, check out our reviews of the countertop water filters including countertop reverse osmosis filters. With three different categories to choose from, it’s possible to have filtered water anywhere!
Faucet Types
There are two types of pure water faucets available with an under sink reverse osmosis unit: a standard dedicated faucet and an air gap faucet. Note, in some municipalities, it is mandatory to install an air gap faucet with an RO system, although this is widely ignored. Some sinks will have a covered hole, spray hose opening, or integrated soap dispenser that can be used for your dedicated RO faucet.
A standard dedicated RO faucet usually requires a ½” to 5/8” hole. The air gap faucet, however, usually requires a 1 ½” opening and this can be beyond the scope of DIY skills, especially if a hole has to be drilled through the counter top. This requirement may affect your choice of RO system. Once the hole for the dedicated faucet has been solved, the remaining installation is very straightforward.
Installation Process
The top under sink reverse osmosis systems that we recommend use press fit quick connectors for the water tubes, which provides a good joint without the need for any special tools or knowledge. This process describes the installation process, which is generally more complex than installing countertop systems and may require some DIY skills.
Although there are slight differences from system to system, under sink installation is generally as follows:
- Turn off and disconnect the cold water feed pipe from the wall to the faucet with the shut off valve.
- Attach the supplied ‘T’ connector to the cold water feed outlet.
- Reconnect the cold water feed to the ‘T’ connector (and if necessary, the push fit connector – in some cases, it may already be attached).
- Drill a hole in the waste pipe for the filter waste connector. In our experience, we found that having the drain connector on a horizontal section of waste pipe reduced the noise when the system is flushing.
- Using the drill bit as a guide, attach the RO drain connector to the drain pipe.
- Attach the RO system filter package to the side wall of the cupboard or back wall. Make sure that there is enough room in all directions to remove the filters and perform maintenance. Some systems require a large, plastic wrench to loosen filter housings.
- Place the reservoir tank on the base of the cupboard.
- Install the filter faucet on the top of the sink, which may require drilling into the countertop.
- Attach all of the water tubes. In most cases, the pipes are color-coded to ensure that the correct connections are made.
- If a UV light system is present in the system, plug it into the electrical outlet. You may need an electrician if you don’t already have power available.
- Turn the source cold water on at the shut off valve and check for leaks throughout the water path.
- Fill and empty the reservoir 3 to 4 times (the exact amount of times depends on the individual system).
The system is now producing filtered reverse osmosis water.
After initial installation, it is worth checking the system every day or so for leaks. If the system remains leak free for a while, then check every month to make sure that no leaks occur. After installing any plumbing system, it is recommended to check for leaks daily for the first few days and monthly thereafter.
Maintenance
All RO systems will, from time to time, need periodic maintenance and the intervals are dependent on the type of system that you have and on the quality of the water that enters the filters. Maintenance intervals for filtration systems depend on water quality, and pre and post filters typically need changing every 6 to 12 months. Timely filter change and regularly changing the filters are essential to maintain water quality and ensure the system operates efficiently.
Pre and post filters will need replacing every 6-12 months or by your usage volume. Manufacturers have recommended schedules but the most effective way to know for sure is to test the water before and after it is processed by your system. You can do this yourself with a simple TDS meter. Some reverse osmosis systems also include filter life indicators, which remind users when it’s time to replace filters, making maintenance easier and helping to protect water quality.
All RO membranes have a life span of between 1 and 5 years. Again, the better the quality of the feed water the longer the membrane will last. One area that will help extend the life to the membrane is to make sure to always change the pre-filters membranes when needed.
The process varies by manufacturer although most RO systems have easy to change filters. In some cases, all that is needed is to lift the filter slightly out at the base, press a button on the holder and the filter comes away. Other filters pull out and the replacement just pushes in. Finally, there are the types of filters that are contained in housings. These housings are unscrewed so that the filter cartridge can be replaced and then the housing is screwed back into place.
Apart from spending a few minutes every few months replacing old filters, the rest of an under sink reverse osmosis system is maintenance free.
Reverse osmosis systems can last over 10 years with proper maintenance and timely filter replacements.
Environmental Impact and Sustainability
Reverse osmosis systems are not just a smart choice for your health—they’re also a win for the environment. By installing a reverse osmosis water filtration system at home, you can dramatically cut down on your use of single-use plastic bottles. In fact, a single RO system can replace thousands of plastic bottles each year, helping to reduce plastic waste and the pollution that comes with it. This means you can enjoy great-tasting, purified drinking water straight from your tap, while also making a positive impact on the planet.
The design of your RO system also plays a key role in sustainability. Traditional systems with a storage tank can waste several gallons of water for every gallon of purified water produced. However, the latest tankless systems have set new standards for efficiency—wasting as little as one gallon for every three gallons of purified water. This not only conserves water but also reduces the energy needed to treat and deliver water to your home.
When it comes to replacement filters, many manufacturers are stepping up their sustainability game. Some offer recyclable filters or even filter recycling programs, making it easier to minimize waste. Plus, advances in filter technology mean longer filter life, so you’ll need to change them less often. For example, certain systems now offer filters that last up to two years, which means fewer replacements and less waste over time.
Using reverse osmosis at home can also support broader improvements in municipal water quality. As more households rely on home water filtration systems, the demand for bottled water drops, allowing cities to focus resources on enhancing the safety and taste of tap water. RO systems are especially effective at removing heavy metals, chlorine, and other harmful contaminants from city water, providing an extra layer of protection for your family.
Energy efficiency is another plus. Most reverse osmosis units use about as much power as a small LED light bulb, making them a cost-effective and eco-friendly choice compared to the energy-intensive process of producing and transporting bottled water.
NSF/ANSI Certification ensures the system effectively removes contaminants like lead and PFAS.
In summary, reverse osmosis systems offer a sustainable solution for anyone looking to improve their water quality while reducing their environmental footprint. With efficient water usage, recyclable replacement filters, and the ability to eliminate the need for bottled water, an RO system is a smart investment for your home and the planet.
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