The 5 Best Under Sink Reverse Osmosis Systems

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Not all reverse osmosis systems are created equal. The difference between the best RO systems and average ones are quite drastic. It can mean the difference between purity of the water and  frequency of maintenance. Keep reading to learn our top recommendations.

We recommend that you read this whole article. If you can’t, our experts recommend APEC Water Systems Reverse Osmosis System.

-The Green Pinky

Why do you need the best under sink reverse osmosis system? It’s simple – water. It’s the life force of all living things.

Having purified, clean water is of utmost importance to humans and plants. There have been countless stories of unclean water sources that have resulted in cancer in certain communities. Under sink reverse osmosis systems solve this issue. Here on this page you will find the best under sink reverse osmosis systems based on our review of dozens of reverse osmosis systems and also reading multiple user ratings.

I’ve compiled an easy to read table below with the best under sink reverse osmosis systems. Included in the chart are the dimension of the product. Make sure that you have enough space to fit the system under your sink!

Comparing Our Top 3 Recommendations for Reverse Osmosis Systems

Best reverse osmosis under sink

The Best Under Sink Reverse Osmosis Systems

Here are my top picks for under sink reverse osmosis systems. Please keep reading for short reviews of each product. Also make sure to continue reading below for some things to look for when you are buying your reverse osmosis system as well as installation tips. You will be on your way to pure water soon!

Undersink reverse osmosis

Best Under Sink Reverse Osmosis Systems

APEC 5-Stage Ultra Safe Reverse Osmosis System ROES-50

The APEC 5-Stage Ultra Safe Reverse Osmosis System ROES-50 can deliver between 30 and 50 gallons of clean, filtered, softened water per day with its under sink system. The long-lasting filters help to reduce contaminants such as fluoride, bacteria, lead, arsenic, chlorine, and heavy metals by up to 99 percent. The system, which is simple to install at home, also comes with a lead-free faucet fixture for even safer water. In addition, the system is made of high-quality pieces with leak-free fittings and food grade tubing, so homeowners can rest assured that their under sink reverse osmosis system will provide clean, safe water for many years. 

APEC RO-90 5-Stage Water Systems Ultimate Series Reverse Osmosis System

One of the best ways to enjoy fresh, safe, filtered and softened water at home it with the APEC RO-90 5-Stage Water Systems Ultimate Series Reverse Osmosis System. This system is durable and designed to last for many years. In addition, the filters are large and are made to filter out two times more contaminants with less filter changes and fewer clogs. The system rids water of up to 99 percent of harmful contaminants such as chlorine, arsenic, heavy metals, lead, and fluoride, so homeowners are left with cleaner, better tasting water that is completely safe to drink or use in cooking. Best of all, this system is designed not only to be easy to install but also easy to identify and replace anything that isn’t working at its most efficient over time.

iSpring RCC7 5-Stage Reverse Osmosis System

The iSpring RCC7 5-Stage Reverse Osmosis System easily mounts under the sink to provide clean, safe, tasty drinking water that is held in the system’s 3.2 gallon tank. Installation is designed to be simple and quick, but if homeowners need extra assistance, expert help is always available. The system’s components are designed to be durable and long lasting, and the high quality also helps to ensure that little routine maintenance is required. In order to see that the system is working properly, a clear stage one housing makes it easy to inspect the filtration with just a glance. Homeowners who use this system will find that their water is clearer and tastes better due to the system’s ability to remove up to 99 percent of over 1,000 contaminants, including lead, asbestos, and arsenic.

Express Water 5-Stage Reverse Osmosis Water Filtration System RO5DX

The Express Water 5-Stage Reverse Osmosis Water Filtration System RO5DX is one of the best options when it comes to producing water that tastes great and is safe and healthy to drink. This system removes up to 99.99 percent of contaminants with a coconut carbon filter that is environmentally friendly. The system removes nitrates, chlorine, lead, fluoride, calcium, arsenic, and bacteria for softer water that tastes better when making coffee, tea, ice cubes, soups, pasta, or simply when having a glass by itself. The system is also easy to install and can be done without professional help, although expert support is available anytime assistance is needed.

iSpring RCC7AK 6-Stage Under Sink Reverse Osmosis System with Alkaline Remineralization

For a system that effectively removes up to 99 percent of 1,000 different contaminants, the iSpring RCC7AK 6-Stage Under Sink Reverse Osmosis System with Alkaline Remineralization is an excellent choice. Many reverse osmosis systems remove both contaminants and healthy minerals. However, the iSpring system has an additional sixth stage, where water is re-mineralized. This means that the system removes contaminants such as fluoride, calcium, sodium, arsenic, asbestos, lead, and chlorine, but then restores the beneficial minerals so that water is cleaner and safer but also tastes natural. In addition, the system is easy to install and fits conveniently under a standard kitchen sink. The system is also built to last and is designed to be durable and reliable, with only low maintenance required.

Under Sink Pure Water

Reverse Osmosis Guide​

When you are deciding on the best possible under sink reverse osmosis system, there ae a couple things to consider. To make the best decision, you need to understand a little about the process of how it works. Alternatively, you can check out any of the reverse osmosis systems above.

In the following sections, I’ll explain some of the common terms and how it works.

What is Reverse Osmosis and How Does It Work?

Osmosis is a naturally occurring process where a weaker saline solution will tend to migrate towards a stronger saline solution. Many plants and cellular functions rely on osmosis for homeostasis.

Reverse osmosis describes a process that is used to filter and purify water. The purification process passes water through a semi-permeable membrane that removes the unwanted particles. In contrast to osmosis, which occurs naturally, reverse osmosis requires energy. You need to force water through these semi-permeable membranes with high pressure pumps to counter the forces of osmosis. The water that is left over that contains all the contaminants is known as the reject.

Unlike other water filtering systems, reverse osmosis is able to remove small particles. The filtered water’s quality will be better with reverse osmosis.

Reverse Osmosis water

What to Consider When Buying an Under Sink Reverse Osmosis System?


The reverse osmosis systems above are all designed to go under the sink. Note that these systems still require quite a bit of space though. Make sure that the area under your sink can fit the system. You also will likely need to rearrange or remove any objects you had been storing under the sink. Don’t make the mistake of buying a system that is too big for your space.

Water Pressure

Reverse osmosis systems rely on water pressure to provide the external forces to push the water through the semi-permeable membranes. Many reverse osmosis systems need at least 40 or 45 PSI to function properly. Some of the reverse osmosis systems come with booster pumps that can increase the pressure of your waterline.

Water Usage

Reverse osmosis systems consume large amounts of water. The reject water that contains the contaminants is more than the water that becomes filtered. In areas where droughts frequently happen, reverse osmosis systems may not be a great option because the amount of waste water.

Replacement Filters

As with all other water filtering systems, reverse osmosis systems will need occasional maintenance. Reverse osmosis systems often use more than one filter, so you will need to keep track of how often each respective filter needs to be changed.

Why Does It Matter?

Water that undergoes reverse osmosis is filtered of its contaminants. This can make a huge difference in quality depending on your water source. More and more often, tape water is not safe to drink anymore, even in cities with “high quality water”. A surprising amount of American’s water (80+%) contains contaminants that have been linked to cancer.

Reverse osmosis filters out dangerous contaminants such lead, arsenic, nitrates, nitrites, chromium, bacteria, viruses, fluoride and many more chemicals. A reverse osmosis system is able to remove 99.99% of contaminants.

Hydroponic Applications

Using water that has undergone reverse osmosis is very important for hydroponic growers as well. Plants grown in hydroponic systems rely entirely on the water and the nutrients has to be finely calibrated. Plants that are grown traditionally have soil to act as a buffer in case nutrients are not perfect. This is not the case with hydroponically grown plants unfortunately.

As such, the water for hydroponic systems need to be tested for pH and ppm. However, if you simply use tap water which has ions, chemicals, and particles, your baseline ppm will already be off. It will be impossible to then try to add the right amount of nutrients as you won’t be able to effectively get to the exact ppm you want.

Installation and Maintenance of Reverse Osmosis systems

Reverse osmosis systems all require installation into your facet before it works. They are designed to be permanently installed with connections into the cold water feed and waste pipes under a sink.

The installation of these systems should be relatively easy with some basic DIY skills and tools. The only difficult part would be drilling a hole in the counter for the filtered water faucet (if one does not already exist).

Air Gap Faucet vs Standard Faucet

Air gap faucets provide a siphon break, which means that if the sink accidentally backs up, there is no way that the dirty water can be siphoned back into your reverse osmosis system. In some areas, it is part of the plumbing code to require the use of air gaps faucets (but this is not common). In these municipalities, for better or worse, this is widely ignored. Air gap faucets usually require much bigger openings. If a hole needs to be drilled through a counter top, this may be too difficult for the average DIYer.

Standard faucets usually require a 0.5 inch to 5/8 inch hole, which is much more manageable.

Installing Reverse Osmosis System

The best undersink reverse osmosis systems use press fit quick connectors that allow for quick connection without requiring any special tools.

Please refer to the instructions that comes with the system that you buy. Generally, the installation process is as followed

  • Turn off and then disconnect the cold water feed pipe from the wall to the faucet.
  • Attach the T connector to the cold water feed outlet
  • Reconnect the cold water feed to the T connector
  • Drill a hole in the waste pipe along the horizontal section of your waste pipe for the filter waste connector. By doing it on the horizontal portion this usually decreases any flushing noises.
  • Attach the drain connector to the drain pipe.
  • Attach the filter package to the side wall of the cupboard. Make sure there is enough room to remove filters for maintenance checks and filter replacements.
  • Place the reservoir tank on the bottom of the cupboard
  • Install the filter faucet on the top of the sink.
  • Attach all of the water tubes.
  • Turn on the water and check for leaks.
  • Fill and empty the reservoir 3 times before use.

You can also refer to the Youtube video below (not my personal video, but it gives pretty clear instructions) for a general guide as to how to install the reverse osmosis system.

Bottom Line

Again, I recommend buying the APEC 5-Stage Ultra Safe Reverse Osmosis System ROES-50​. Do not be fooled, the difference between a good reverse osmosis system and an average one is huge. It can mean tons of extra dollars and hours spent on repairs. That being said, you cannot go wrong with any of the above reverse osmosis systems. They are the best systems that you can find available on the market. 

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About the author: Carley Miller is a horticultural expert at TheGreenPinky. She previously owned a landscaping business for 25 years and worked at a local garden center for 10 years.

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