How to Choose an Under Sink Water Filter

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

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Under sink water filters are excellent choices for those looking for a great mix of filtration capability and practicality. However, with so many choices available, it can be hard to determine which one works best for you.

If you are not sure how to choose between one type and another, this guide is what you need.

It will walk you through the different types of under sink water filters available, their advantages and disadvantages, and the factors you need to consider before choosing one.

So, here is our guide on how to choose an under sink water filter!


  • You must take your water quality into account when selecting the right under sink water filter.
  • Select a system that can get rid of the water pollutants you are dealing with. Tip: Make sure to choose under sink water filters that have NSF certifications for the particular contaminants you have in your water source.
  • Reverse osmosis, multi-stage, and single-stage systems are available for different levels of pollution.

Under Sink Water Filter Types

You can choose from several different types of under sink water filters, sorted according to their filtration methods and design. Some options might be better suited to your home based on the amount of space you have and how contaminated your water supply is.

The different types of under sink filters are:

Single-Stage Filters

A single-stage under sink water filter uses only one stage of filtration to purify water that passes through it. While it might seem inadequate, this is actually more than enough for many people’s needs. Because activated carbon is usually applied, they are especially effective for eliminating bad smells and odors.[1]

Multi-Stage Systems

A multi-stage under sink filtration system filters your water through a series of filter elements, each designed to handle a specific type of contamination. As a result, they are more effective at purifying more severely contaminated water but also come with some downsides, such as a higher average price and taking up more room.

RO Systems

Reverse osmosis uses pressure to forcefully push water through a delicate membrane. Most larger molecules are pushed back and remain on the entry side of the membrane, which is specially designed to allow only water molecules to pass through.

While reverse osmosis membranes are excellent in dealing with certain types of contamination, such as high TDS levels[2], they are often less effective in removing chemicals for example, when compared with other filtration methods. For this reason, RO systems for home use usually feature additional pre-filtration.

Inline Design vs. Separate Dispenser

Some models also come with an attached faucet that you have to install. This is useful in situations where it is difficult to attach an inline filtration system to the existing plumbing. But, it requires more space. Adding the faucet will also require extra work due to the need to open a hole to run it through.

How to Choose an Under Sink Water Filter?

How to Choose an Under Sink Water Filter Thumbnail

You must first identify the contamination levels you are dealing with and your particular home situation to choose the right under sink water filter.

Besides, even if you were to have the cash to buy a multi-stage model, you need to verify that you have enough space for it under your sink. And there’s more!

Here are all of the factors you’ll need to consider before choosing an under sink water filter:

What Purification Methods Are Right for Your Water Quality?

First, you need to find out what the water quality in your house is like.

  • You can order a DIY test kit to get a rough idea of the situation.
  • Specialized laboratories provide more detailed information but are also more expensive and take longer.
  • It might also be possible to check local water quality reports depending on where you live.

NSF/ANSI Certifications: Is the Filter Certified?

An NSF certification can be a valuable tool for identifying the type of contaminants an under sink water filter is designed to remove.

However, often they don’t tell you much about the exact filtration capabilities of the filter, just that it removes certain contaminants above a specific reference level.

Filtration: Which Process Works Best for You?

You may need to invest in a reverse osmosis filter system or another type of multi-stage under sink water filter if your water is heavily contaminated.

Generally, those provide the best overall filtration but are also more expensive. A single-stage activated carbon filter can get the job done if you don’t need heavy contaminant removal.

Filter Stages: Single or Multi-Stage?

You need to consider how many filtration stages you’ll need. As mentioned before, a single-stage filter will probably do the trick if your water isn’t too heavily contaminated. However, a multi-stage setup will be necessary if you have high level of contaminants or need to handle a wide variety of types.

Water Flow Rate & Pressure: How Much Water Do You Need?

You should pay attention to output flow rate and pressure in large households with many thirsty family members. An under sink filter that is too slow will not provide your family with enough water on demand.


If you know your plumbing setup and have some common household tools, installing an under sink filter is not very complicated. In the case of a filter with a dedicated faucet, you will have to make an opening for the faucet, among other things.

Price: What is Your Budget?

An under sink water filter’s initial purchase cost is not the only expense you’ll have to deal with over its lifetime.

The cost of filter replacements, which can become quite expensive quite fast with some models, must also be taken into account.

When it comes to things like repairs, sometimes buying a more expensive model is worth it.

Filter Life and Maintenance: How Much Will You Pay in the Long Run?

Consider how often you should replace your filter cartridges. In the long run, certain seemingly simple models can prove to be very expensive when their filters need to be replaced frequently. On the other hand, buying a higher-priced unit usually results in lower long-term maintenance costs.

Space: Where Are You Installing the System?

under sink water filter being installed

While you will rarely see your under sink water filter on a daily basis, it will still require some space. These systems are one of the most convenient options because they do not occupy much “usable” space, though. You’ll find them under your sink, tucked away from view and not in the way of your daily activities.

This is especially true for multi-stage filtration systems. Make sure you check the dimensions of each model you’re considering if you live in a smaller home. You should also check how your plumbing is laid out, as sometimes you may not be able to fit an under sink filter, even if you have enough free space because it’s impossible to hook it up to your existing plumbing without major modification.

Pros and Cons of Under Sink Water Filters

These are the advantages and disadvantages of using under sink water filters:

The Pros

1. Simple Installation and Maintenance

An under sink water filter is easy to install and maintain and does not require specialized tools or experience. Those with a dedicated faucet are the only exception, but most people can handle even those.

2. User-Friendly

The way that water filter pitchers and other countertop models are used can make them cumbersome for kids and the elderly. Under sink models don’t require you to do any heavy lifting or move anything around, making them ideal for these consumers.

3. Compact

An under sink water filter normally resides in an area that is not used for anything other than storing cleaning agents and similar items, so it has a very small impact on your comfort level. This can be beneficial in small households with limited space, as a countertop filter can easily take up a double-digit percentage of the available space.

The Cons

There are only two downsides to under sink filters:

1. Not Enough Water for Large Homes?

Typically, larger households have multiple water faucets for drinking. A single under sink water filter cannot cover them all, so you’ll need to purchase a separate filter for each exit point.

In addition to the upfront cost, the replacement cost of the filter, which can quickly pile up, makes buying multiple under sink water filters even pricier.

2. Drilling May Be Required

If you opt for a model with a dedicated faucet, you have to do some additional work for its installation. This can be a bit of a problem if you lack confidence in your handy skills, requiring you to seek help from a professional.


While under sink water filters are excellent choices for most households, there isn’t a universal option for all situations.

Single-stage filters work great when you don’t have a lot of space, but they are less powerful than multi-stage setups when it comes to their filtration capabilities. On the other hand, going multi-stage is more expensive and requires more space.

You also need to consider the long-term maintenance costs and your house’s water pressure. If you carefully evaluate all factors, you will certainly choose an under sink water filter that fits your needs.

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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