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Types of under sink water filters explained

By: Craig Smith
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Types of under sink water filters explained

Your tap water is disgusting and undrinkable, and you’ve decided to get an under-sink filter to do something about it. 

That’s a great start! 

But now you have to figure out what kind of filter to get.

There are several good options available to clean up your tap water. You no longer have to put up with drinking water that is just two steps above pond water. You’ll also no longer need to dump half of your paycheck into bottled water each week. 

Don’t let all the types of under-sink filtration systems available overwhelm you, we’re here to explain them to you. Keep reading to find out the differences between the different designs of under-sink water filters and hear more about how they work.

What Is an Under-Sink Water Filter


Water filters, in general, remove sediment and other contaminants from your water to make it more drinkable. They produce better-tasting, healthier drinking water. 

An under-sink water filter is a type of filter designed to connect to your existing cold water line under your kitchen sink. They sit in the cabinet below the sink. Some connect to your existing faucet, some come with their own faucet.

Each home may have different contaminants in the water supply. There are different types of under-sink water filters to specifically target the contaminants in your water. 

If your water has a lot of heavy metals, there are filters specifically for that. Have smelly or bad-tasting water? There are under-sink water filters for that. 

Under-sink water filters are very customizable. By using the right filtration cartridges or selecting a multi-stage filter, you can adapt to match whatever is in your water supply.

What Are the Types of Under-Sink Water Filters Available? How Do They Work?

The different types of under-sink water filters are best described by the filter medium and the number of stages. Let’s take a look at these factors.

Single Stage

A single-stage under-sink water filter is one that has a single filter media type. These waster filters generally target a specific contaminant, or sometimes several. They are generally not as flexible as multi-stage under-sink water filters, and they may not remove all your water contaminants if you have a particularly dirty water supply. 

Single-stage under-sink water filters are great for cleaning up specific contaminants and improving water taste and smell. They offer easy installation, easy maintenance, and are usually more affordable than multi-stage filter systems.

A single-stage under-sink water filter can use a range of filter cartridges. Filter cartridges are often interchangeable, meaning you can swap from one type to another if your needs change. We describe the most common filter cartridges below.


Sediment filters are probably the most common type used in single-stage systems. They are a basic filter, and do a good job at filtering out sediments, dirt, salts, and some chemicals. 

A sediment filter is rated by pore size, listed in microns. Think of it as a screen, letting very small particles through and stopping larger particles. 

You’ll often see filters listed as 5-micron filters, for example. The smaller the size, the more it filters out. 


There are several types of carbon filters available, and all do a good job of removing chemicals from your drinking water. In some ways, carbon filters are more advanced than the sediment filters above. 

Granular Activated Carbon

Granular activated carbon filter cartridges contain loose granules of carbon. The granules absorb the molecules of contaminants, letting the water pass through. 

They are effective at removing chlorine, chemicals, and organic compounds, and leave you with better tasting and better smelling water. These water filters have very little impact on the water flow rate.

Cabon Block

Carbon block filters are made of similar materials as granular activated carbon. Particles of carbon, often in the form of charcoal, are ground into granules that are many times smaller than the granular activated carbon, then pressed into a solid block. These blocks have openings that are much smaller, sometimes as low as 0.5 microns.  

Not only do they remove the same compounds that activated carbon filters do, carbon block filters also remove bacteria. They are usually more efficient than granular carbon. Keep in mind, these water filters can reduce water flow.

Catalytic Carbon

This is another type of carbon filter. It’s more effective than granular carbon, and is very good at removing the chemicals and VOCs from your water. One thing a catalytic carbon filter excels at is removing chloramines.


KDF filters use a redox reaction to clean your water. Redox stands for reduction-oxidation. It’s essentially a chemical reaction that changes harmful impurities into harmless substances.

KDF is made from a copper-zinc blend. They are a great way to remove heavy metal, chlorine, and hydrogen sulfide. You’ll often see these combined with other filter types in mult-stage systems.


Ceramic filtration works by using natural ceramic media. The ceramic has tiny pores, sometimes as small as 0.5 microns. Water passes through these pores, filtering out bacteria and sediment in the process. 

The ceramic is often impregnated with silver ions, which does a great job of sterilizing the water and killing bacteria.

Iron Filter

Iron filters work by converting dissolved iron into larger particles of rust, which then become trapped in the filter media. 

These are a perfect addition to a multi-stage filter, but don’t do much to remove things like sediments and chemical compounds.


Ion-exchange filter cartridges work by swapping ions of the contaminants with ions in the resin in the filter cartridge. This is typically sodium or hydrogen.

These filters are good at removing certain contaminants like arsenic, sulfates, and other inorganic substances. 

Activated Alumina

Activated alumina filters contain granules of activated alumina, which the water passes through. Contaminates are absorbed into the activated alumina. 

They can remove things like arsenic, sulfates, fluoride, thallium, and uranium from your water.


Multi-stage filters are essentially two or more single-stage filters connected inline. This lets them use multiple types of filter cartridges, providing cleaner water in the end.

Many multi-stage under-sink water filter systems start with a sediment filter and often include a carbon filter after that. 

This kind of filter system may have several filter types, and could use a variety of combinations to target your specific contaminants. That makes them very customizable, since all you need to do is swap to different filter cartridges.

Reverse Osmosis


Reverse osmosis systems work differently than a standard under-sink water filter system. RO systems are some of the most effective water filtering systems available. 

But reverse osmosis systems are also some of the most expensive of all water filter systems available.

The way a reverse osmosis system works is by forcing water through an RO membrane. This membrane has incredibly tiny pores, allowing it to filter out the majority of contaminants. 

Pores can be as small as 0.0001 microns. By the time water passes through the RO system, it is almost entirely pure.

There are downsides to a reverse osmosis water purification system. For one thing, RO systems come with a high price. 

They always require their own dedicated faucet, so you must have space for that. Many people complain that their water tastes flat when using a reverse osmosis system. 

Do I Need an Inline Filter or a Dedicated Faucet?

Under-sink water filters can connect to your existing faucet, tying into your cold water inlet. This is called an inline filter. When you have this type of connection, all cold water that flows through the faucet goes through your filter. 

That means that you may be using filtered water to wash your hands or rinse a plate, not just for drinking and cooking.

An under-sink water filter may use a dedicated faucet instead. You typically place this faucet alongside the existing faucets. Many sinks already have a cutout for this. 

The advantage of the dedicated faucet is that you only use up the filter capacity on water you really need filtered. You can get your water to drink or cook from that faucet, but still use regular tap water when washing your hands. This will extend the life of your filter and save you money.

How Long Do Under-Sink Filters Last?

How long under-sink water filters last varies, depending on how much water you use and the type of filter you have. The average is six months.

Most under-sink water filters come with a manual that will tell you how often to change the cartridges. They often list this as the number of months between changes. If you use a lot of water, you’ll need to change the cartridges more often. 

Some under-sink water filters have cartridges that may last a year, others only three months. Highly contaminated water will impact this as well, so if your water is particularly dirty then you’ll need to change the filters more often.

By changing your cartridges on time, you’ll have a continuous supply of clear, purified water.

Are Under-Sink Water Filters Worth It?

Whether under-sink water filters are worth it depends on your circumstances, but many people think they are. They’re relatively affordable, easy to install, and can last for many years. 

For most under-sink water filters, your only ongoing costs will be replacement filters. That makes them far cheaper than constantly buying bottled water, and better for the environment. On top of that, you’ll end up with healthier and better tasting water.

In Conclusion

We’ve discussed the different types of under-sink water filters and given you some idea of what each type removes. Using this information, you should be able to make a more informed decision on what under-sink water filter is best for you. 

Check out the best under sink water filters here.

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Craig Smith
Craig got his start in water working in the swimming pool and spa industry. Water treatment would grow into his main career but he ended up working in the pool industry for over 26 years where much of his time was spent balancing the water in customer's swimming pools and installing water filtration equipment. Craig offers an abundance of water treatment knowledge after helping homeowners get pure water for 26 years.

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