How to Choose an Under-Sink Water Filter

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So, you’ve decided to install an under-sink water filtration system to improve your water quality and taste. Great choice! Under-sink systems offer one of the most convenient, effective on-demand water filtration solutions.

But the market for under-sink water filters has grown significantly in the past few years, and we now have more choice than ever – almost too much choice, if you’re not a water filtration expert.

In this guide, we’ve shared our top tips for choosing an under-sink water filtration system that’s ideal for your budget and your needs.

📌 Key Takeaways:

  • When choosing an under-sink water filtration system, consider your budget and your water quality before anything else.
  • Make sure you’re aware of the different under-sink water filters available:
    • Single-stage systems
    • Multi-stage systems
    • Reverse osmosis filters
  • Select a system based on the contaminants you want to remove.

📝 Choosing an Under-Sink Water Filter System: What To Consider

Ready to buy an under-sink water filter for your home’s tap water supply? Here’s what you should consider, in this order:

Your Budget

First of all, consider how much you can afford to spend on an under-sink water filter system.

Most under-sink filtration systems cost $100-$650 upfront. The system cost depends on the type of system, the number of filter stages, and whether or not the system has advanced features, such as built-in pressure gauges and filter-change reminders.

Also consider what you can afford to spend on maintenance per year. The filter replacement cost for under-sink systems is $50-$150 on average, depending on the number of filters and the filter life.

Filter TypeSystem CostAnnual Maintenance Cost
Single-filter systems$50-$100 $50-$75
Dual-stage filter systems$150-$400$100-$200
RO under-sink filters$150-$1,000$100-$250

Your Water Quality

Your water quality is an equally important consideration to make.

The contaminants your water contains determine which types of under-sink water systems are best.

For instance, if your water’s biggest quality issue is chlorine, a single-stage activated carbon block filter may be all you need.

But if your water contains heavy metals like lead, nitrates, and other dangerous impurities, you’ll probably want to look at a more advanced filter.

Test a sample of your water with a laboratory water test to find out exactly what it contains.

Testing tap water with Tap Score

Your Design Preferences

There are a few different filter designs to consider when you’re searching for a suitable under-sink system.

Faucet vs No Faucet

Some under-sink units connect to your existing cold water line and faucet, while others come with their own dedicated faucet.

Filters with dedicated faucets provide the reassurance of no recontamination, while using your own metal faucet may cause metals to leach back into your filtered water.

However, dedicated faucet filters require a bit of extra installation.

Installing an under sink water filter dedicated faucet

RO Tankless vs Tank-Based

RO under-sink filters are either tank-based or tankless.

Tank-based units have a water storage tank. They take up more room, but they store filtered drinking water and provide instant access to this water when you turn on the faucet.

Tankless systems are smaller and more space-saving, but they filter water on demand, so you’ll have to wait slightly longer for filtered water to leave the tap.

Waterdrop G3P800 under sink RO filter change

NSF Certifications & Testing

Third-party testing for contaminant removal is a reassuring sign that an under-sink filtration unit performs as expected.

Even better if the manufacturer has obtained official NSF certifications for its performance. This tells you that the system has met stringent NSF standards for removing specific impurities.

Required Flow Rate & Water Pressure

Most under-sink systems have a flow rate of 0.5-2.5 GPM.

The slower the output water pressure, the slower the water flow from your faucet. Make sure to choose a system that can keep up with your water pressure flow rate requirements.

Your Installation & Maintenance Preferences

Installing an under-counter water filter is usually pretty easy, as long as you have some basic DIY skill and plumbing knowledge.

You’ll just need to hook the system up to your cold water feed line. Systems with a dedicated faucet and tank-based RO systems are slightly more challenging to install.

🚰 Types of Under-Sink Water Filter Systems:

Not sure what types of under-sink systems you have to choose between? We’ve outlined them below:

Single-Stage Water Filters

Best suited for: Mild contamination

Single-stage water filters use a single filter stage to remove a handful of the most common contaminants in tap water.

Most single-stage systems use a carbon filter that may or may not be combined with other filter media, such as KDF media or ion exchange resin.

These filters are ideal for reducing bad smells, tastes, and odors in tap water.

Multi-Stage Water Filters

Best suited for: Moderate contamination

Multi-stage under-sink systems combine several filter stages (usually 2 or 3) to remove a broader range of harmful contaminants from tap water.

The filter stages may include a sediment filter, several types of carbon filters (such as activated carbon block filters and granular activated carbon filters), and other media, like KDF and ion exchange.

Clearly filtered under sink direct connect system

Reverse Osmosis Water Filters

Best suited for: Severe contamination

The most expensive and thorough under-sink filtration option is reverse osmosis.

An RO system combines multiple filtration stages with a reverse osmosis membrane to remove almost all impurities from water.

These systems offer the best protection against all contaminants, but they’re too expensive for some budgets and remove healthy minerals, which gives water a “flat” taste.

⚖️ Pros and Cons of Under Sink Water Filters


Provides Filtered Water On Demand

The biggest benefit of an under-sink filtration system is that you get access to clean, filtered water on demand.

Simply switch on your faucet and wait for water to travel through the filters. In a matter of seconds, you’ll have clean water on tap.

Easy to Install & Maintain

Compared to whole home filters, under-systems are easy to install at your cold water line. In most cases, you just need to install a T valve to direct water through the filter before it leaves your faucet. You shouldn’t have to hire a plumber for the job.

Maintenance is easy, too. Just snap or twist out the old filters and put the replacement filters in their place.

Suitable For Most Budgets

There are various kinds of under-sink systems, and you should find something that’s suited to your budget.

A single-stage under-sink filtration system costs as little as $150 or less. Or, if you have a bigger budget to play with, spend $200+ on a multi-stage system, or $450+ on an under-sink reverse osmosis system.

Replacing an under sink water filter

Hidden & Space Saving

Most under-sink filter systems are small, compact, and easy to store underneath your kitchen sink.

The best systems have an all-in-one design that only takes up a fraction of your under-sink shelf space.

Plus, because they’re designed for under-sink installation, these filters won’t be an eyesore in your kitchen.


Some Designs Require More Difficult Installation

Certain kinds of under-sink systems are more complex – and require a more difficult installation – than others.

For instance, reverse osmosis systems need to be connected to a drain line, and many RO systems have a water storage tank. Some under-sink units also come with a separate faucet that needs to be installed alongside your existing faucet.

More Expensive Than Other POU Options

If your budget is small, or you’re new to water filtration and hesitant to spend a lot of money, under-sink filters might not be the best choice for you.

There are much cheaper options (costing less than $80), such as faucet filters, some countertop filters, and water pitcher filters, that might be more accessible to you than under-sink systems.

Reduce Flow Rate

Even the best under-sink filters decrease flow rate somewhat. Generally, the more filter stages, and the more thorough the filtration process, the slower the output water flow rate.

If you’re happy to wait a few more seconds to fill a glass of drinking water, a slightly reduced flow rate shouldn’t be an issue for you.

Reduced amount of water passing through the ro system

🤔 What’s The Best Under-Sink Water Filter System For Me?

Now you know the types of under-sink water filters available and the key considerations to make before making a purchase, you should find it easy to choose the best under-sink water filter for you.

Decide on whether you prefer a single-stage, multi-stage, or reverse osmosis filter system based on what your water contains and how much money you have to spend.

💡 Want to know what the experts recommend? Our best under-sink water filter reviews should point you in the right direction. 👈

Other Filters To Consider

Under-sink water filtration systems are super convenient, giving you access to filtered water from your faucet on demand.

But they’re not necessarily the best choice for you.

If you’re stretching your budget even for a single-stage under-sink filter, consider a water pitcher filter instead.

Water pitcher filters are cheaper than under-systems and offer a similar performance. The only setback is that they don’t provide filtered water on demand. It takes up to 20 minutes for a pitcher to filter a full batch of water.

If you prefer to filter your entire water supply, consider upgrading to a whole home water filtration system.

This system is essentially an oversized version of an under-sink system, but it’s installed at your water line where it enters your home, meaning that your entire plumbing system is protected against water contaminants.

Clearly Filtered water pitcher on countertop

❔ Choosing an Under-Sink Water Filter: FAQ

Are under the sink water filters worth it?

Under-the-sink filters are worth it for you if your water contains chlorine, heavy metals, and other common contaminants, and you want an affordable, on-demand filtration system. If you want the cheapest way to filter drinking water, under-sink systems might not be right for you – look at faucet-mounted filters or pitcher filters instead.

How do I choose the right water filter?

You can choose the right water filter by considering which filter is best suited to you based on your water quality, your budget, and your contaminant removal needs. Read expert guides and customer reviews when deciding whether or not a certain filter or brand is worth your money.

Is a pitcher or under-sink filter better?

An under-sink filter is better if you want on-demand water filtration, but a pitcher is best if you don’t mind waiting for your water to be filtered and you prefer a portable, more affordable filtration solution.

What are the setbacks of under-sink water filters?

Some of the setbacks of under-sink water filters are that they reduce your water flow rate, they sometimes need a separate faucet, and they’re more expensive than most other POU filtration options.

  • Jennifer Byrd
    Water Treatment Specialist

    For 20+ years, Jennifer has championed clean water. From navigating operations to leading sales, she's tackled diverse industry challenges. Now, at Redbird Water, she crafts personalized solutions for homes, businesses, and factories. A past Chamber President and industry advocate, Jennifer leverages her expertise in cutting-edge filtration and custom design to transform water concerns into crystal-clear solutions.

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