Types of Under Sink Water Filters

Interested in buying an under-sink tap water filter? Want to know more about your options before you start comparing products? You’ve come to the right place.

In this guide, we’ve shared everything you need to know about the different under-sink filter models and the types of filter cartridges they could include. We’ve also answered your frequently asked questions about the best, cheapest, and most expensive under-sink filtration systems.

🤔 What Are Under-Sink Water Filters?

Under-sink water filters are units that are installed underneath your kitchen sink, with the purpose of delivering clean drinking water out of your faucet.

An under-sink filtration system intercepts your existing cold water line. Water flows through the filter media, and contaminants become trapped inside the filter. When water leaves the system, it has been filtered – so any harmful contaminants have been removed.

Under-sink filtration systems rely on water pressure to send water through the filter media. This means they don’t need to be connected to an electricity supply, and they provide almost instant access to filtered water.

🚰 3 Different Under-Sink Water Filter Models

The three most common under-sink filtration models are single-stage units, multi-stage systems, and reverse osmosis systems.

Single-Stage Units

As the name suggests, single-stage units are filtration systems that consist of a single filter stage. These tend to be the most affordable water filter systems for under-sink use, and offer targeted filtration that focuses on a select type of contaminant or group of contaminants.

Single-stage units are beneficial for anyone dealing with a specific water quality issue, but they’re not as thorough as multi-stage systems.

Multi-Stage Systems

Multi-stage systems are under-sink filters that consist of two or more filter stages. Most multi-stage filters have three separate filtration stages, each targeting a different set or size of contaminants.

Multi-stage systems are a good option for people who want to remove more than just a handful of contaminants from their water.

Reverse Osmosis Systems

Reverse osmosis systems are multi-stage units that feature a semi-permeable membrane. A reverse osmosis system purifies water and eliminates virtually all total dissolved solids. This system is the most expensive type of under-sink filter available.

RO systems are ideal for people who want to remove as many contaminants as possible from their tap water. Typically, reverse osmosis filters have three filter stages and their own separate faucet.

📰 The Different Types of Under-Sink Water Filters

Now you know the different under-sink filter models, let’s look at the types of water filters that could be included in these systems.

Sediment Filters

Sediment filters are typically the first filter stage in multi-stage or reverse osmosis under-sink filters.

A sediment filter traps large particles of sediment, dirt, dust, and rust, preventing them from damaging later filter stages. The three common types of sediment filters are depth, surface, and absorptive filters.

The standard pore size of a sediment filter is 5-10 microns, meaning that contaminants larger than 5-10 microns are trapped, while smaller contaminants can pass through (these will be trapped in later filter stages).

Carbon Block Filters

Carbon block filters are made from powdered carbon, compacted together into a solid block. These filters typically have a micron rating of 0.5-1.0, so they’re capable of removing tiny contaminants that might slip through the pores of other filters, like cysts and bacteria.

Because of their compacted design, carbon block filters have a longer contact with water than activated carbon filters, which allows them to trap more contaminants at once.

Granular Activated Carbon Filters

Granular activated carbon cartridges, or GAC filters, are commonly used as a second or third stage in multi-stage under-sink water filtration systems. They may also be used in a single-stage under-sink system, either alone or blended with other filter media, like KDF or ion exchange.

GAC filters use adsorption and chemical reactions to pull contaminants like chlorine, chemicals, disinfection byproducts, and pesticides out of water.

Catalytic Carbon Filters

Catalytic carbon filter cartridges are designed to remove chloramine from tap water. Chlorine is more persistent in water than chlorine, and is more difficult to remove. A standard activated carbon filter doesn’t remove chlorine, but catalytic carbon can.

A catalytic carbon cartridge is either used in a single-stage water filtration system or is featured as a second or third stage in a multi-filter unit. This media also reduces hydrogen sulfide in water.

KDF Filters

KDF filter cartridges are made from a blend of copper and zinc and reduce contaminants using a reaction known as redox. These filters are rarely used alone – they’re either used alongside carbon cartridges in multi-stage systems, or they’re blended with carbon in a single-stage filter.

Depending on the filter type, KDF removes contaminants like lead, chlorine, mercury, hydrogen sulfide, and chromium. The design of KDF filters prevents the growth of bacteria.

Ion Exchange Resin

Ion exchange resin offers target contaminant removal by exchanging ions of opposing charges. Like KDF, ion exchange is often combined with sediment and carbon filters in multi-stage systems because it removes two contaminants that a carbon filter can’t touch: arsenic and sulfate.

Ion exchange resin is not the same as the ion exchange process that softens water in a water softener. Hardness minerals aren’t removed by an ion exchange under-sink resin.

Activated Alumina Filters

Activated alumina is another specialist type of filter that’s commonly blended with carbon or used alongside carbon in a multi-stage under-sink filtered water system. This filter consists of a bed of activated alumina granules, which adsorbs difficult-to-remove contaminants like arsenic, uranium, fluoride, and thallium.

Activated alumina is the only filter media that’s specifically designed to remove fluoride, so it’s an ideal solution for fluoridated water.

UV Purifiers

UV purifiers aren’t technically water filters, as they don’t remove contaminants with a filtration process. Instead, they send ultraviolet light into water, which damages the DNA of microorganisms like bacteria and viruses, preventing them from causing harm. UV can only target living organisms, and can’t be used to physically remove impurities.

UV purifiers are typically installed in a whole house filter system, but they can also be used as add-ons to single- or multi-stage under-sink filtration units.

Semi-Permeable Membranes

Semi-permeable membranes are found in RO under-sink filters. These membranes have a pore size of 0.0001 microns and are capable of trapping most existing contaminants, from heavy metals to bacteria and everything in between.

Semi-permeable membranes are combined with other RO filters, like carbon and sediment filters, in an under-sink RO system. This enables the RO system to produce pure water, but there are some disadvantages to this – water is wasted in the RO process, and healthy minerals are removed.

⏳ Under-Sink Water Filters Lifespan

Different under-sink filters have different lifespans, depending on their capacity, filtration methods, surface area, pore size, and quality.

Your water quality and water usage also affect the lifespan of an under-sink unit. You might need to buy replacement filters for your system every 6 months, while somebody else might only buy a filter replacement filter every 9 months.

Typically, the lifespan of sediment filter cartridges is 6 months, while carbon cartridges have a filter life of 9 months, and post or polishing filters last for 12 months.

🧫 What do Under-Sink Water Filters Remove?

The contaminants targeted by an under-the-sink filtration system depends on the media used in the filtration process.

Common contaminants removed by the best under-sink water filter systems are:

• Chlorine taste and odor
• Chloramine
• Lead and other heavy metals
• Pesticides
• Herbicides
• Disinfection byproducts
• Nitrite
• Nitrate

A specialty under-sink filter system might be capable of removing additional contaminants, like:

• Bacteria
• Viruses
• VOCs
• Pharmaceuticals
• Radon
• Fluoride
• Arsenic

Under-sink RO systems also remove beneficial minerals and salts, like calcium and magnesium, from water.

Check out this post to learn about the best under sink filters for use with well water.

🆚 Under-Sink Systems Vs Other Filter Types of Water Filters

A filtration system installed underneath your sink is only one of the types of water filters you can buy.

Below, we’ve listed some of the other types of water filtration options, and how these compare to under-sink units.

• Water Pitcher Filters – Cheaper but slower than under-sink units because they use gravity, not water pressure, to filter water.
• Countertop Filters – Similarly priced but take up more space than under-sink units.
• Whole House Filters – More expensive than under-sink units but filter your entire hot and cold water supply.
• Faucet-Mounted Filters – Much cheaper than under-sink units but affect water flow rate and have a short filter lifespan.
• Refrigerator filters – Cheaper than under-sink units but have shorter lifespans.

Related: Whole house water filter vs under sink filters full comparison

🧠 Types of Under-Sink Water Filters FAQs

What’s the best under-sink water filter system?

The best type of under-sink water filter for contaminant removal is a reverse osmosis filter. However, most people don’t want to remove all total dissolved solids from their water. If you just want to target the most common drinking water contaminants, the best under-sink system for you is an activated carbon filter. We published a complete guide so you can learn how to select an under sink water filter, read it here.

What’s the cheapest under-sink water filter?

The cheapest filter for under your sink is a single-cartridge filtration system. You can buy these filters for around $100 or less.

What’s the most expensive under-sink water filter?

The most expensive under-sink water filter is a reverse osmosis filter system. RO systems often cost $400 or more.

What are the best under-sink water filter system brands?

We’ve reviewed dozens of under-sink water filter systems, and some of our top current brands are Clearly Filtered, Aquasana, and Epic Water Filters.

What are the benefits of under-sink units?

Water filters under your sink are connected to your existing cold water line, so they give you instant access to filtered municipal water without having a big impact on your water flow rate. By removing chemicals, heavy metals, and other contaminants, they improve water taste and quality. Most are designed for easy installation, too.

How long do under-sink water filters last?

Under-sink water filters have an average lifespan of 6-12 months, depending on the filters included in the system. The units themselves have a 5-10 year lifespan or longer, but you may need to replace certain components, like the valves and o-rings, before then.

Are under-sink water filters worth it?

It depends on what you want from a filter. Under-sink water filters are worth it if you’re looking to enjoy filtered drinking water on demand. These filters aren’t necessarily the right choice for you if you want to filter your entire water supply, or you have a small budget and want to spend as little as possible on a water filter.

Are all water filter cartridges the same?

No. All water filter cartridges are made differently. Even two activated carbon cartridges made by different brands will have different designs, surface areas, pore sizes, lifespans, and contaminant reduction abilities. That’s why it’s important to shop around and buy a filter based on exceptional customer feedback, rather than because you’ve heard the type of filter cartridge is supposed to be good.

Can you buy under-sink water softeners?

No. Water softeners are one of the few water treatment options that can only be installed at your home’s point of entry. This is largely because of their intended use: water softeners are designed to soften your entire home’s water supply. If you installed a water softener underneath your kitchen sink, you’d only be protecting your under-sink cold water line from limescale, rather than the pipes, faucets, and appliances around your whole home.