Under Sink Water Filters vs. Reverse Osmosis Systems

Author: Rory Mullan - Published: 2022/08/05 - Updated: 2022/12/22

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If you are looking for convenient water filter systems, you’ll probably come across two options: under sink water filters and reverse osmosis systems. Both offer great filtration capabilities, but the way they work is quite different.

We got exactly what you need if you are unsure which one to choose.

This article will explain how under sink and reverse osmosis water filters work, their advantages and disadvantages, and the factors you need to consider before choosing one.

So, here is our guide on under sink water filters vs. reverse osmosis systems!


  • Reverse osmosis systems and under sink water filters are not that different from one another.
  • While RO systems usually require pre and post-filtration in addition to the reverse osmosis membrane, under sink water filters might use one, two, or more filter stages.
  • Generally speaking, a reverse osmosis system reduces contaminants more effectively overall but also costs more money. Advice: Get a water test to find out what pollutants are present. Based on the outcomes, make your purchase selection.

What Are Under Sink Water Filters?

An under sink water filter is a general one-stage or multi-stage filtration system designed to be mounted underneath your kitchen sink, hooking up to your plumbing before the water is dispensed from the faucet.

They are a great way to optimize your home’s layout since they are relatively inexpensive and don’t get in the way.

under sink water filter being installed

How Do Under Sink Water Filters Work?

Under sink water filters filter water before it reaches the faucet by attaching it to the cold water line. This makes them simple and convenient, giving you instant access to filtered water.

The effectiveness and quick operation of under sink water filters is what makes them very popular. In addition, they are less expensive than whole house water filters.

Removing Contamination

An under sink water filter’s ability to remove contaminants depends on the type of filtration applied. The simplest models filter your water using only one filter element. In contrast, multi-stage models use multiple types of filter media to maximize contaminant reduction.

Thus, contaminant removal varies from one water treatment system to another, so it’s important to identify the models that target the specific contaminants you’re concerned about.

Benefits of an Under Sink Filter

1. Relatively Small

For most people, an under sink water filter’s small, compact design is one of its main attractions. In most cases, they can fit under the sink and don’t require any plumbing changes. It may be necessary to run your pipes slightly differently in some rare instances to accommodate the filter’s shape, though.

2. Essential Minerals Remain in Water

In contrast to reverse osmosis systems, under sink water filters are designed to target contaminants only. All essential minerals, such as calcium[1], remain unaffected. Therefore, they are a good choice for homes with high mineral content water.

3. Affordable and Easy to Find

Reverse osmosis systems are more expensive and less widely available than regular under sink water filters. This makes shopping for the latter a lot easier.

Drawbacks of an Under Sink Filter

1. May Not Be as Effective as Reverse Osmosis

An RO system is often the best solution if you want your water filtration to be as thorough as possible.

2. Single Point of Use

Except in rare circumstances, connecting one filter to multiple faucets is impossible. For homes with more than one drinking water faucet or access points, there needs to be a separate under sink filter for each. This can result in an exorbitant price tag.

What Are Reverse Osmosis (RO) Systems?

In recent years, reverse osmosis has grown in popularity as a water filtration method for home use. These systems are known for their special semipermeable membrane, which filters out most contaminants from water.

Reverse osmosis filters come in a variety of shapes and sizes and can be easily adapted to standard plumbing connections.

under sink reverse osmosis system with storage tank

How Do RO Systems Work?

The reverse osmosis stage involves forcing water through a membrane containing microscopic holes designed to prevent anything larger than a water molecule from passing through. This leaves almost all contaminants at the input end of the membrane.

Typically, a reverse osmosis system is composed of several steps, with the semipermeable membrane only being one part of the overall process.

Water is usually pre-filtered before it reaches the RO membrane. And a system may also conduct post-filtration to ensure all impurities are removed.

RO systems are available in a variety of configurations:

  • Countertop RO systems
  • Under sink RO systems
  • Whole house RO systems

Removing Contamination

The best thing about reverse osmosis systems is their consistent, thorough contaminant removal capabilities. Oftentimes, the best way to make sure that your water is as clean as possible if you live in an area plagued by heavy contamination is with an RO system.

Benefits of a Reverse Osmosis System

1. Exceptional Water Purification

Right now, reverse osmosis is one of the best water filtration methods available to consumers. It is thorough and effective, leaving almost nothing but H2O behind. As a result, it is ideal for cases where the water supply contains a variety of contaminants, making conventional filtration expensive and prone to failure.

2. Customization

Depending on the user’s needs, a reverse osmosis system can be adapted to many different configurations. You can always find a filtration device that fits your needs, no matter what shape it takes.

Drawbacks of a Reverse Osmosis System

1. Costly

The average cost of a reverse osmosis system is higher than other filtration methods, including a multi-stage under sink water filter. Investing your money in a regular under sink filter may be better if you have a lower budget.

2. Mineral Loss

The biggest disadvantage of reverse osmosis is that it doesn’t select what it removes from the water, as it targets anything that can’t pass through the RO membrane. Because of this, it also removes some beneficial elements.

3. Time-Intensive Process

RO water treatment is a very slow process. This is why under sink units come with their own storage tanks.

4. A Lot of Moving Parts

A reverse osmosis system consists of several components, including a check valve and an automatic shut-off valve. As a result, it’s more prone to issues than a simpler under sink filtration system.

5. Wastewater

Any RO system wastes water during the purification process. Some waste less, some waste more.

Is RO-Purified Water Healthy?

Reverse osmosis systems might compromise the quality of your drinking water if your home has a water supply that is rich in minerals. This is because the filter removes many useful nutrients and regular contaminants.

If you are considering RO water purification, make sure you check reports about the quality of your current water and remineralize if need be.

Similarities & Differences of Under Sink Water Filters and RO Systems

Under Sink Water Filters vs Reverse Osmosis Systems Thumbnail

Under sink water filters and reverse osmosis systems differ mainly in their filtration method. Although reverse osmosis systems can be packaged as under sink models, most standard under sink filters use a more basic treatment process, like activated carbon.

Apart from that, they both work in the same way – they attach to your plumbing and filter the water that passes through them before it reaches a point of access.

Remember This When Shopping

Do you prefer thorough filtration that captures all types of contaminants present in your water supply, or do you only care about a few types? This is a question you must ask yourself before making a choice. When deciding between an under sink water filter and a reverse osmosis system, you should consider filtration strength.

You should also think about how much space you have in your home. The compact design of a single-stage under sink water filter makes it ideal for smaller households. There are smaller versions of reverse osmosis systems, but they tend to be bulkier in general.

If you want to find the right balance between filtration quality and physical size, it is ideal to consult an expert who can guide you through the purchase process.


Under sink water filter vs. reverse osmosis system; a few factors make the choice much simpler for you.

For instance, if you have limited space, you are probably better off with a single-stage under sink filter. This is doubly true if you have water with high mineral content, as RO filters won’t discriminate between one solid particle and another.

However, reverse osmosis is the way to go if you need a filtration system that captures all contaminants. Just keep in mind that it is a slower process than other filtration methods.

Further Reading


Meet Rory Mullan

Rory Mullan Rory has joined the Water Masterz team as a contributing writer. He has covered all sorts of topics in the last several years.

Outside of his writing work, Rory enjoys photographing the Irish landscape and making music!

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