Shopping for an under-sink reverse osmosis system?
You’ve come to the right place.
Reverse osmosis is the most effective way to purify drinking water at home.
Unlike ordinary carbon-based filters that only remove chlorine and other chemicals, an RO system filters out pretty much all contaminants from water, including tough ones like heavy metals and germs.
An under-sink reverse osmosis system connects to the incoming cold water line under the sink and produces purified water from a dedicated faucet.
What's In This Buying Guide?
In this in-depth buying guide, we review the best under-sink reverse osmosis systems in the market.
We also tell you everything you need to know about RO systems, how they work, how to choose the right one for your needs, and how to install an RO system under your sink.
If you are looking for a different type of RO system, read our best reverse osmosis systems buying guide for reviews of the countertop, portable, and other types of reverse osmosis filters.
Best Under-Sink Reverse Osmosis System 2020: Comparison Table
Home Master TMAFC-ERP
- Editor’s top pick
7-stage with non-electric permeate pump
Express Water RO5DX
- Best budget
5-stage with a leak-stop valve to prevent flooding
Home Master TMHP
- Best for well water
9-stage with UV protection and a permeate pump
- Best tankless RO System
7-stage with booster pump and space-saving tankless design
Tier1 Essential Series
- Best RO Filter/Softener
Combined 5-stage RO system and whole-house water softener
- Best for large families
5-stage with long-lasting filters
Best Under-Sink Reverse Osmosis System 2020: Reviews
Home Master TMAFC-ERP Artesian Reverse Osmosis Water Filter System
Home Master TMAFC-ERP is a high-performance under-sink RO system that removes up to 98% of contaminants in water.
It has seven stages of filtration.
A sediment filter reduces particulates. Carbon filters remove chlorine and other chemicals, and an RO membrane eliminates impurities such as heavy metals, fluoride, TDS, and bacteria.
The Home Master TMAFC-ERP stands out from other RO systems in several ways.
For one, it uses catalytic carbon filtration instead of the usual active carbon filters. This makes it more effective at removing chloramines (which active carbon struggles to filter out) and other chemicals.
Another unique feature is double re-mineralization. Most RO systems have one mineral/alkaline filter.
The Home Master TMAFC-ERP RO system has two. It adds small amounts of calcium and magnesium to the water at two points during filtration.
Adding back health minerals stripped from the water improves the taste of the water and makes it better for your body.
Home Master’s filter design is also a bit different. Instead of the usual configuration where the filter cartridge is in a housing, the TMAFC-ERP uses a modular design where the filter cartridge and housing are one.
When replacing the filter, you dispose of both the housing and cartridge. It has several benefits:
Another great feature worth mentioning is the integrated Fast Flow RO Kit that significantly improves the amount of water flowing out of the RO faucet. You don’t have to wait forever to fill up a water bottle or jug.
Like other RO systems, the Home Master TMAFC-ERP ‘wastes’ some water when it’s working. This water is used to clean the RO membrane and flush contaminants down the drain.
Thanks to a built-in, permeate pump, the Home Master TMAFC-ERP drains away much less water than other RO filters. Its waste to pure water ratio is 1:1, compared to the inefficient 4:1 ratio of other systems.
The filter lifespan is one year (or about 2,000 gallons) for the pre-filters and 3-5 years for the RO membrane.
Issues & Limitations
The Home Master TMAFC-ERP is a great choice for anyone looking for a high-performance, reliable, and low-maintenance under-sink reverse osmosis filter.
Express Water Reverse Osmosis Water Filtration System
If you are on a budget, we recommend the Express Water RO system. It’s one of the cheapest under-sink RO filters around. Still, it purifies water just as effectively as pricier RO systems.
The compromises you have to make for the lower price include a lower daily capacity (50 GPD instead of the usual 75-100 GPD) and a lack of a re-mineralization filter.
Just because it’s cheaper than most RO filters, it doesn’t mean the Express Water RO system removes fewer contaminants.
The lower price is because it lacks some bells and whistles that are not essential to filtration.
When it comes to removing impurities, the Express Water RO system is just as good as pricier RO filters.
A 5-stage filtration process removes over 99% of impurities. The pre-filters – sediment filter and two carbon filters – filter out particulates, chlorine, and various chemicals.
An RO membrane then removes heavy metals, TDS, fluoride, and microorganisms.
Just before the water comes out of the faucet, it passes through a carbon post-filter to clean up any residual smells and tastes from the water.
The Express Water RO system misses several components available in higher-priced systems. But these are not essential and, if you want, you can add them to the RO system later.
These include a permeate or booster pump to increase water efficiency and output, an alkaline filter to add healthy minerals to the water, and a UV filter to provide additional protection from microorganisms.
The Express Water RO system is fairly easy to install. You can set it up yourself in 2-3 hours.
Issues & Limitations
The lack of an alkaline filter or permeate pump is not a big deal since you can add these yourself. What you cannot change, however, is the short filter lifespan.
The Express Water filters last about half the time of other RO filters. The pre-filters are good for just six months, while the RO membrane lasts only one year.
The Express Water RO system is a great choice for anyone looking for a high-performance but affordable under-sink reverse osmosis filter.
Home Master TMHP HydroPerfection Undersink Reverse Osmosis Water Filter
All RO systems can purify well water. But filter life is significantly reduced because of damage from iron and other contaminants found in groundwater.
The Home Master TMHP HydroPerfection RO system is designed specifically to handle well water without any damage to the filters. It has an iron pre-filter to remove all types of iron and a UV filter to kill germs.
The iron pre-filter is what makes the Home Master TMHP HydroPerfection a good choice for homes that use well water.
The KDF85 media removes dissolved iron from the water before it reaches the RO membrane.
Other pre-filters include a sediment filter to remove particulates and catalytic carbon filters that reduce chlorine, chloramines, and other chemicals.
The RO membrane deals with all other remaining contaminants, including the high level of TDS usually found in well water, heavy metals, and microorganisms.
The Home Master TMHP HydroPerfection also comes with a UV filter that complements the RO membrane in neutralizing bacteria, viruses, and other harmful microorganisms.
Similar to other Home Master RO systems, the TMHP HydroPerfection uses long-lasting filters. The pre-filters last one year while the RO membrane is good for 3-5 years. The UV filter needs to be replaced after a year.
The Home Master TMHP HydroPerfection undersink RO system has an efficient 1:1 waste to pure water ratio, thanks to the built-in permeate pump that reduces how much water goes down the drain.
It is far more efficient than other RO systems, which have a ratio of 4:1.
Another area where the Home Master TMHP HydroPerfection outdoes other RO filters is the faucet flow rate. The Fast Flow RO kit doubles the normal water flow rate.
Installing the Home Master TMHP HydroPerfection is a 2-3 hour DIY job. Everything you need is included.
Note that the system may be a tight fit under the sink. You can lay the reserve tank on its side to save space.
Issues & Limitations
The Home Master TMHP HydroPerfection is more expensive compared to most under-sink RO systems. But for the extra cost, you get an iron pre-filter for well water and a UV filter to kill germs.
So, overall, we think it’s worth it.
Waterdrop Reverse Osmosis Drinking Water Filtration System
The biggest component in a conventional under-sink reverse osmosis system is the reserve tank. The tank can be hard to fit even under a spacious kitchen sink.
That’s why the Waterdrop RO tankless system is such a space saver. It’s a single compact unit that fits easily even in a small under-sink space.
It’s not just the absence of a tank that saves space; the Waterdrop system also uses an innovative filter design.
Instead of separate filter housings linked with tubing, Waterdrop’s filters fit into the main unit.
The integrated design saves more space and makes filter replacement much easier compared to the traditional RO systems.
Despite the compact design of the Waterdrop system, it has as many filtration stages as traditional filters.
The three composite filters add up to seven filtration stages.
First filter: Two Sediment pre-filters + a carbon block pre-filter. These remove sediment, chlorine, and various chemicals.
Second filter: Three layers of the RO membrane remove over 99% of heavy metals, TDS, and heavy metals.
Third filter: The final filter consists of just one post carbon filter to clean up any remaining odors and tastes.
The Waterdrop RO system has an electric pump that boosts the pressure of water going through the filters.
The pump also ensures a strong flow rate out of the faucet and an efficient 1:1 waste to pure water ratio.
Another way the Waterdrop filter stands out is the digital control panel that indicates two things: filter life and TDS levels. The TDS indicator tells you how well the RO system is working.
Other Waterdrop features we love include:
Issues & Limitations
The main issue many customers have with the Waterdrop RO system is the price. Even without a tank, it costs more than traditional RO systems. But many say it is worth it.
Another issue is that it requires an electrical connection to work. You may need to call an electrician to add an outlet under the sink if you don’t have one.
Keep in mind that the filter will not work if there’s a power outage, something you never have to worry about with conventional RO systems.
Tier1 Essential Series 48,000 Grain Water Softener with Under Sink Reverse Osmosis System
Buying an RO water filter + water softener combo will save you money compared to purchasing each separately.
Our top combo pick is the Tier1 Essential Series water softener and RO system. The water softener treats all the water coming into your home while the RO system goes under your sink to purify your cooking and drinking water.
Reverse osmosis does a great job removing TDS (total dissolved solids) from water. These include calcium and magnesium, the primary minerals that cause water hardness.
If an RO filter can soften water, why do you need a water softener?
The problem is that hard water quickly damages an RO membrane. Scale forms on the membrane, reducing its output and reducing its lifespan. Instead of the usual 2-3 years lifespan, you’ll have to get a new RO membrane every 3-6 months.
The Tier1 Essential Series combo solves this problem by combining a water softener and an under-sink RO system.
The water softener softens all the water coming into your house. It’s a whole-house water softener.
The under-sink RO system can then purify the softened water without damage to the membrane. Not only will you get better quality water, but your RO system and filters will also last longer.
You can choose between a 32,000-grain and 64,000-grain softener depending on your family size. The water softener comes with everything you need, including a brine tank, resin, mineral tank, bypass, and fittings. The only thing you need to buy is salt for the brine tank.
A digital control head monitors water flow and triggers automatic regeneration. You can also set the head to trigger regeneration when it’s least disruptive, typically at night.
The reverse osmosis system uses five filtration stages to purify the softened water. They include three pre-filters, an RO membrane, and a post-filter.
The RO system removes any remaining TDS as well as heavy metals, chlorine, chemicals, and microorganisms.
Issues & Limitations
You can install the Tier1 Essential Series water softener and RO system yourself, but it takes time – 3-4 hours on average. The poor instructions certainly don’t help.
Many customers had to call customer support for guidance on installation.
Some found it easier to hire a pro to install the two systems, but that means spending extra money.
Something else to note about the Tier1 Essential Series combo system is that it is not ideal for well water. It cannot handle water with a high level of iron (more than 3 ppm). Groundwater typically has lots of dissolved iron.
If you use well water in your home, the manufacturer recommends installing a whole house iron filter. Install it before the water softener.
The Tier1 Essential Series water softener and RO system is a great choice for homeowners looking for a combined water softener and reverse osmosis system at an affordable price.
APEC RO-90 Supreme Reverse Osmosis System
Need a lot of RO purified water for drinking, cooking, and other uses? Get the APEC RO-90 under-sink reverse osmosis system.
It has one the highest daily outputs among RO filters – 90 gallons vs. 50-75 of other RO systems.
Most RO systems average about 50 to 75 gallons of purified water output per day. That’s enough drinking water for most families.
But larger families might need more than that, especially if you also use the water for pets, cooking and other uses.
The APEC RO-90 under-sink system produces more purified water per day than most RO filters – up to 90 gallons.
It is a five-stage system, consisting of three pre-filters, an RO membrane, and a post-filter.
The pre-filters include double carbon blocks that remove almost all chlorine, chloramines, and other chemicals from water.
The membrane reduces TDS, heavy metals, fluoride, and bacteria while the post-filter polishes the water to remove any tastes and odors still in the water.
Issues & Limitations
The APEC RO-90 system comes with a 4-gallon pressurized tank with a usable capacity of 3.2 gallons. The small tank does not take full advantage of the system’s high output.
You may occasionally run out of purified water and have to wait for the tank to fill up again.
For a more stable water flow, we recommend upgrading to the 14-gallon or 20-gallon APEC tank.
Another limitation that may require an upgrade is the flow rate. The water flows out slowly from the faucet, especially as the water level in the tank goes down.
To solve this, you’ll need a booster pump. It’ll increase water flow from the faucet and also reduce the amount of water the system’ wastes’.
APEC RO-90 is a great choice for large families that need a lot of purified water for drinking and other uses.
Specification Chart: Top Picks Compared
|RO System||Dimensions||Weight||With pH Filter||Capacity (GPD)||No. of Stages||Reserve Tank Water Capacity|
|Home Master TMAFC-ERP ||12 x 16 x 20 inches||14.5lbs||Yes||75||7||3.2 gallons|
|Express Water RO5DX ||16.2 x 18.8 x 18.1 inches||30.8lbs||No||50||5||3.2 gallons|
|Home Master TMHP HydroPerfection ||12 x 16 x 20 inches||18.75lbs||Yes||75||6||3.2 gallons|
|Waterdrop||18.1 x 5.7 x 17.8 inches||31lbs||Yes||400||7||None|
|Tier1 Essential Series||18.5 x 18 x 18 inches (RO system only)||111lbs (RO system + softener)||No||50||5||3.2 gallons|
|APEC RO-90 ||16 x 5.2 x 17.5 inches||25lbs||No||90||5||3.2 gallons|
Do You Need an Under-Sink Reverse Osmosis System?
To decide if you need an under-sink RO system, you just need to answer one question: are you worried about germs or heavy metals in your drinking water?
If you are, then yes, you need an under-sink RO system. An RO system is the only type of residential water filter that can reduce heavy metals and waterborne bacteria and viruses in your water.
What if you are only worried about chlorine in your water? A cheaper carbon filter can help with that. It can also remove chemicals such as VOCs, pesticides.
What about fluoride? Here you have two options. You can use an RO system or an activated alumina filter.
If your concern is only about fluoride, an activated alumina under-sink filter like Home Master TMJRF2 Jr F2 is cheaper than an RO system.
But if you also worried about germs, heavy metals, and other impurities, an RO system is the best option.
Here the bottom line: If you want the safest drinking water, get an under-sink reverse osmosis system. An RO system removes the most contaminants from water, including heavy metals, bacteria, chemicals, and sediment.
The Definitive Buyer's Checklist: What to Consider When Choosing an Under-sink RO System
1. Number of Stages
The number of stages represents the number of filters in an RO system.
The minimum number of stages an under-sink RO system should have is five. These include three pre-filters (a sediment filter and two carbon filters), an RO membrane, and a post-filter.
The pre-filters remove sediment and chemicals to protect the RO membrane from damage.
The membrane reduces tough impurities like heavy metals and bacteria, and the post-filter gives the water a final polish.
Some RO systems have seven or more stages. These extra stages are not essential to filtration performance but are nice to have. They improve the quality and taste of water.
The two most common extra stages of looking for include a mineral filter and a UV filter.
A mineral or re-mineralization filter adds small amounts of minerals to the RO purified water to improve the taste. Re-mineralization also balances the water’s pH or makes it slightly alkaline. pH-balanced and alkaline water is better for your body than acidic water.
A UV filter complements the RO membrane in reducing microorganisms in your drinking water. If you are worried about waterborne bacteria and germs (especially if you use well water), an RO system with a UV filter provides the best protection.
2. Daily Output
Next, check how many gallons of purified water the RO system can produce per day. For most families, we recommend a 75 GPD (gallon per day) RO system. Smaller families will do with a 50 GPD RO filter, while larger families should get a 90 GPD or higher RO system.
Note: If you use RO water for other uses other than drinkings, such as gardening, pets, and skincare, you’ll need a high-output RO system.
3. Filter Life
Finally, check the filter life. Filters with a short lifespan can raise maintenance costs since you need to buy new filters often.
Note that pre-filters and the post-filter have a different lifespan from the RO membrane.
The minimum lifespan for the pre-filters and post-filter should be six months. The ideal lifespan is one year.
The minimum recommended lifespan for the RO membrane is 2-3 years. Premium models like Home Master use high-quality membranes that can last 3-5 years.
Tip: Make sure you buy your RO system from a reputable and well-known company to ensure you can easily find replacement filters.
How To Install an Under-Sink Reverse Osmosis System
Before you do anything, check that the package has all the parts you need. If anything’s missing or broken, contact customer support.
RO systems come with colored tubes so you can easily tell which one goes where.
All you need to do is connect the main feed line to your cold water supply using the included T connector.
Use quick connectors to run the tubes from the cold water supply to the RO system, then to the storage tank, the faucet and the drain saddle.
You’ll need to drill a hole in your sink for the faucet. But if you have an unused hole, you can insert the RO faucet there.
Once you’ve installed the RO system, drain the first couple of tanks to flush the system.
Note: Check your manual for specific installation instructions.
Care and Maintenance of Under-Sink Reverse Osmosis Systems
Reverse osmosis systems are low-maintenance. The only thing you need to do is replace the filters after 6-12 months and the RO membrane after 2-3 years.
Occasionally check the system for leaks, especially where the quick connectors are located.
Frequently Asked Questions About Under-Sink Reverse Osmosis Systems
What impurities do reverse osmosis systems remove?
RO systems use multiple filters to reduce chlorine, chemicals, microorganisms like bacteria, heavy metals, fluoride, and sediment.
Which impurities does a reverse osmosis system NOT remove?
Reverse osmosis does not remove some chemical solvents, VOCs, and pesticides. Also, an RO system does not remove all microorganisms. Certain bacteria and viruses may pass through.
Is reverse osmosis water bad for you?
RO water is great for you. Even without minerals, RO water is healthy since most essential minerals come from the food you eat.
If you want to make RO water healthier, look for an RO system with a mineral filter. Alternatively, add liquid minerals to the RO water.
Does reverse osmosis reduce TDS?
Absolutely. A reverse osmosis system can reduce TDS by 90% or more. This includes harness minerals, heavy metals and other solids dissolved in water.
Where To Get The Best Deal on an Under-Sink Reverse Osmosis System
Amazon is the best place to get the best deals on under-sink RO systems.
They have a wide range of sizes and brands, and the prices are usually lower compared to manufacturer websites and brick and mortar stores.