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Under Sink Water Filter Review (Here’s Our #1 Pick)

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When it comes to choosing a water filtration system, you want something that is within your budget that gets the job done. Your water should taste purified and smooth once filtered, and while many filtration systems can do this, there are those that do it better than others, removing 98% to 99% of all contaminants from water supplies.

From reverse osmosis systems to filtration with permeate pumps, there are a number of different water filtration brands, but which one offers the best under sink water filter? In this guide, we go over what to look for in the top under sink water filter systems and show you the reviews of our favorite water filters on the market today.

Five Star-Rated Water Filters

Top Pick

Waterdrop G3 P800

  • 7-Stage Deep Filtration
  • Tankless Design with Smart Faucet
  • NSF/ANSI 58 & 372 certified
Top Pick

Frizzlife PD600

  • 7-Stage Deep Filtration
  • Smart LED Display & Quick Change Filters
  • Adds Alkalinity and Essential Minerals

Aquasana OPTIMH2O + Claryum®

  • 6-Stage Filtration
  • Combines Reverse Osmosis & Claryum Technology®
  • Certified to NSF/ANSI Standards 42, 53, 58, 401 + P473

Water filters are an investment for your health, but there are a ton of reasons to get a filtration system for your home or office. We analyzed hundreds of under sink water filter types to find the best options based on contaminants removed, NSF certification, ease of installation, filter life, warranty, and customer satisfaction.

We’ve named our top picks below and included different options based on your home’s water source and water pressure.

Waterdrop Filters G3

We really enjoyed reviewing the Waterdrop G3 RO Filtration System. For one, it removes over 1,000 contaminants and includes TDS reduction. It was also enlightening to see an all-in-one water filtration system that delivered water instantly and continuously without multiple filter storage tanks.

This system can be installed quickly due to its no tank design, and it works with your main faucet. The body is only 5.7 inches wide, so it doesn’t take up much space at all. You get about 400 gallons per day with this system as well.

This is probably the most innovative water filter that we reviewed. We loved the simple, smart design with a white case because it fit in the back of the cabinet and left space for everything else. It also has a smart flashing indicator to show water purification, filter life reminders, and quick connections for effortless installation.

What We Liked

This is truly an all-in-one water under counter water filter system that removes 99% of the contaminants we tested. The water was purified and ready instantly, and it can remove almost every chemical, hard mineral, and micro particles, such as chlorine, rust, colloids, pesticides, lead, arsenic, chromium, fluoride, radium, and sediment.

This system fills up one cup of water in 12 seconds, making it much faster than any of the traditional under sink filters we tested. This is because it has a newer RO under counter water filter system that can filter 400 gallons of water per day.

Best of all, you don’t need a plumber to install the Waterdrop Filters RO system. It has fewer connections and takes seconds to set up, which also reduces the risk for leaks. We looked at customer reviews and found most to be between four and five stars. However, most reviewers commented on the ease of installation and the great taste of the water.

What We Don’t Like

There wasn’t much not to like about this under sink water filtration system. We liked how fast and easy it was to get water, and it was able to purify to a 99% clean rating. In addition, the warranty should cover more than a year.

Exclusive Discount: Save $199 off the Waterdrop G3 with coupon code: AMG3P800

Frizzlife PD600

If you want a budget-friendly under sink water filter brand, Frizzlife offers multiple systems that match this description. In fact, the whole brand centers around affordable, easy-to-install under sink water filtration systems. The Frizzlife PD600 model is the latest from the brand, and it includes a tankless design with an alkaline remineralization stage.

This system comes with multiple filters including a RO filter and remineralization. The sediment filter is actually a 2-in-1 design that removes all dust, dirt, rust, and larger particles before moving into the carbon filters and RO membrane.

It’s a compact and sleek design that comes with a lead-free faucet. The tankless system takes up very little space, while offering a huge increase in flow rate at 600 GPD. We also liked the smart LED display and quick change filter system.

What We Liked

The tankless design is truly convenient thanks to the slim case that FrizzLife included with the PD600. It has the highest rate of filtration out of any of the other FrizzLife products, removing about 97% of all contaminants. While this isn’t as high as some of the other filters, this is great for the value and removes most of the major contaminants, such as chlorine, pesticides, lead, arsenic, and rust.

The alkaline remineralization filter is designed to assist the RO drinking water filter system in replacing nutrients and adjusting your water’s pH to about 7.5. Slightly alkaline water is best as you don’t want anything too alkaline or acidic.

Since this is an all-in-one design, you only need to buy the filter cartridge, so you don’t have to purchase multiple filters throughout the year. It also comes with a dedicated water faucet.

What We Don’t Like

You are beholden to using the water filter cartridges made by FrizzLife, but these are priced pretty reasonably. We also felt that the drinking water filter system could have filtered out more VOCs, but we were satisfied with the results due to its small size and instant flow rate.

Aquasana OPTIMH2O Reverse Osmosis + Claryum®

When it comes to under-sink water filters, Aquasana is a well-known brand. Their OptimH2O AQ-RO-3 water filter delivers 36 gallons per day, purifying 99.99% of all contaminants. While it is a 3-stage water filter, the reverse osmosis (RO) membrane removes almost all toxins, meaning that it’s unnecessary to have 5 or more steps as do larger systems.

That is one of the beauties of this RO under-sink filter: it’s compact and easy to install. During our test, we found that it only took minutes to install and resulted in excellent-tasting water. Thanks to the demineralization filter after reverse osmosis, you always get purified water with nutrients without the toxins.

We wanted to review the OptimH2O system because it is Aquasana’s highest-rated under-sink filtration system, and customers say it’s the best when it comes to purification and water efficiency.


There are a few features that stand out with this system. The OptimH2O comes with a manifold that is lightweight and easy to place under your kitchen faucet. The manifold attaches to the tank and demineralization system with easy access to the filter casing so it is a quick replacement when it’s time to change your filters.

Water Flow

Whenever we review filtration systems, we like to look at how fast and clean the results are. With a 36 gallon per day output and 3.2 gallon storage tank, you’ll get a high output with a 0.8/gpm. This is exceptional for an under sink filter system.

Clean, Purified Water

The filtration system has a 3-stage filtration process with a carbon pre-filter, Claryum post-filter, and reverse osmosis membrane. After going through the RO membrane, demineralization starts, replacing valuable minerals in the water that were removed. Not all under sink filters have this step, so it is an excellent value and enhances the taste.

Satisfaction Guarantee & Warranty

Aquasana offers exceptional customer support for all of their products. Included with the OptimH2O system is a 90-day money back guarantee. In addition, the system is covered by a 2-year manufacturer’s limited warranty.

What We Liked

The best part about the OptimH2O system is that it removes 97% of all chlorine, as well as 99% of all other toxins, including lead, asbestos, pharmaceuticals, cysts, arsenic, and mercury.

Although it’s a 3-state filtration process, the reverse osmosis feature makes it a high-performance filter that removes five times the contaminants in comparison to other under sink systems.

What We Don’t Like

The main issue that we had with this system is that you will need to install a second faucet to get purified drinking water at your faucet. You may have to drill through the counter to install this piece of hardware.

Consider These Before Selecting Under Sink Water Filters

There are differences in filtration systems that are also important to note for your installation. In some cases, filtration systems may not work with your water source or water pressure. It’s best to check these out before you purchase.

Take a look at these factors before purchasing a new water filter:

Water Source

When looking at an under sink water filter, you also have to look at your own connections. This is because an under sink water filter needs the right water source. Most filters are made for city water supply (also known as municipal water supply) or well water systems. If you have well water in your home, then your plumbing is a bit different and may require a different filtration system that includes UV filtration and reverse osmosis. This is due to some of the particular bacteria, iron, rust, chlorine, and sulfates found in well water.

Water Pressure

With any under sink water filter, you want a stable feed water pressure in order for the system to accurately filter your water. You can find the filter’s operating pressure within the specifications online or on the product label. You also want to know your home water pressure specification before purchasing a system.

You may need to get a filter pump if you want higher pressure in your home. The proper water pressure for a single family home is between 40 and 45 psi typically. You will find lower pressure under sink water filter types have a booster pump to increase flow rate.

Filter Effectiveness

Research by the Environmental Working Group revealed that over 300 pollutants were found in water supplies for multiple cities across the US. Many of these were pharmaceutical residues and radioactive particles. In fact, out of all the 20 million drinking water tests from city water municipalities, every single tap water source contained chemicals called trihalomethanes, which are volatile organic chemicals (VOCs). These form when chlorine is added to the water to kill bacteria.

Click image to visit Environmental Working Group’s interactive water quality page

You can judge any filter by its effectiveness at filtering out contaminants. There are some factors that go into knowing just how well a under sink water filter will work.

Carbon-activated filters can reduce most contaminants in water, but if you are looking for micro-filtration for chlorine, chloramines, and lead, then you want something stronger.

Reverse osmosis membrane filtration is a higher step in filtration, but the best systems have a multi-step process that typically looks like this:
• Step 1: Sediment filter
• Step 2: UV Filter
• Step 3: Carbon-activated or charcoal filter
• Step 4: Reverse osmosis membrane

If you do want a reverse osmosis filter, then you should look at filters with low waste to pure water ratio. Traditional RO systems were huge water-wasters when they first hit the industry, which led to a 5 to 1 low waste to pure water ratio. Modern reverse osmosis systems get between a 3 to 1 and 1 to 1 ratio. These systems typically have better feed water pressure or use a special pump to increase water pressure.

Filter Life

You definitely want a system that has long-lasting filters. It’s a pain to change out filters all the time. To minimize your time under the sink, you should look for filters that only need to be replaced once a year or once every two years.

Most carbon and sediment filters need to be replaced 1 to 2 times a year, while RO membranes may need to be replaced once every few years.

Operating Costs

The system costs depend on the number of filtration stages, type of system, and quality of filters. You can expect to pay between $300 on the low end and up to $600 for a high-end RO water filtration system.

Under sink water filters offer many benefits for those who want pure drinking water at any time. For one, you never have to buy bottled water again, and it’s safer to cook with. If you have health problems, alkaline water from in-home filtration could prove to be the best thing for your immune system, too. However, the greatest benefit is that these water filtration systems remove up to 99% of all contaminants.

Final Verdict: The Waterdrop G3 Under Sink Water Filter Stands Out Amongst The Competition

We think it’s best to go with the Waterdrop G3 Reverse Osmosis Water Filtration System. There are many reasons why we like this system, but simply put, it filters out the most contaminants and does not require a whole lot of effort to install. The system fits neatly under the sink and delivers water whether you have low pressure or not. You can easily get pure, drinking water right from the tap without having to worry about anything else, and it comes with a money back guarantee. You won’t find that kind of customer service with many other water filtration companies.

Exclusive Discount: Save $199 off the Waterdrop G3 with coupon code: AMG3P800

What Is Reverse Osmosis?

RO membranes are typically used for an under sink water filter.

If you want an under sink water filter that provides incredibly clean drinking water, reverse osmosis (RO) filtration is one of the best ways to filter water at your home or office. Many water filter systems include multi-step filtration with carbon activated filters and reverse osmosis. When you see “RO” in a filter’s name, it means that water passes through an extra filtration process with a membrane.

How Does Reverse Osmosis Work?

In the simplest terms, reverse osmosis filters out water as it is forced into a semi-permeable membrane, which removes contaminants. These are then flushed back down the drain. Clean drinking water fills up a separate holding tank, which you can access for drinking water with an under sink water filter.

Reverse osmosis systems work with whole house filtration and the under sink water filter. Depending on your household size and how much water you want to filter, either way leads to a 98% or more pure filtered water result.

What Does Reverse Osmosis Remove?

Most water filtration gets between 90% and 95% pure results, but reverse osmosis is one of the best filters to have because of its removal success rate.

RO filtration removes the following contaminants:

  •  Fluoride
  •  Chlorine
  •  Chloramine
  •  Detergents
  •  Lead
  •  Pesticides
  •  Nitrates
  •  Sulfates
  •  Arsenic

Other filters may remove some of these, but because the RO membrane is so thick, it blocks even more contaminants than any other filtration step. That’s why under water sink filter RO types are so highly rated.