Under Sink Water Filter Installation – Step by Step Guide

Author: Jason Hollow - Published: 2021/09/22 - Updated: 2022/11/22

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Under sink water filters are a favorite choice of homeowners because they offer thorough filtration compared to most water filter pitchers and faucet-mounted units. At the same time, their quick installation process isn’t too invasive.

These are low-maintenance cartridge-style units that produce contaminant-free water at a fraction of the price of bottled water.

What’s best is that most under sink water filters do not burn a hole in your pocket. You can purchase a high-quality multi-stage filtration system for as little as $150.

The cherry on top? Since the units are easy to install, you can easily avoid paying extra charges to a professional.

This guide covers all there is to know about installing your little sidekick that will change how your water looks and smells!

So, here is our step-by-step guide on how to install an under sink water filter!


  1. First, shut off the cold water supply.
  2. Detach the tubing.
  3. Install the feed/adapter valve and then reconnect the cold water tubing.
  4. If the filter has a separate dispenser, drill a hole in your countertop or sink in order to install it.
  5. Now put the under sink water filter in place and establish all necessary connections.
  6. Open the cold water supply and let the system flush as you check for any leaks.

Under Sink Water Filter Installation: Preparation

Most reputed water filtration brands will include all necessary supplies required for under sink water filter installation in the package for your ease.

However, there’s no need to fret even if your system does not come with an installation kit. You can easily find all essential supplies at any local hardware shop.

Here is what you need:

  • T-piece connector to cut in the feed water line
  • ¼-inch plastic tubing
  • Water filter wrench
  • Screwdriver
  • A cordless drill with the required drill bits (for the faucet hole)

Since you will be working underneath the kitchen sink, it’s wise to clear out the cupboard and get rid of all the clutter. It will make your job easier if you have a clean space to work on.

Also, you must keep a few old towels or rags handy as you’ll definitely be dealing with water spills. Just place them under the sink so you can access them quickly.

While it is entirely optional, we advise asking a friend or partner for a helping hand. Ready to install your under sink water filter? Let’s go!

How to Install an Under Sink Water Filter System – Instructions

under sink water filter installation thumbnail

The installation process involves connecting your filter to the feed water valve, mounting the system on the wall and drilling a hole in the countertop (if you choose to use a dedicated filtered water dispenser).

If you are replacing an old under sink filter, almost all the work has probably been done for you, and you’ll be free within half an hour. On the other hand, if you are getting one for the first time, you will require one hour to complete the task.

Stay with us as we walk you through the process, one step at a time.

Close Water Supply

So, you are finally on your knees, not for your soul mate but for the water of your dreams! Savor the moment as you turn off the cold water feed valve. If you can’t figure out which pipe is for cold water, turn on hot water on your sink.

Then, touch both incoming water pipes. Naturally, the hot water pipe will be slightly warm to the touch.

Remove Cold Water Tubing

Once the water supply is off, open your kitchen faucet to let as much remaining water and air as possible run out.

Next, disconnect the cold water line from the faucet. Remember, water will still probably come out, so keep your towels handy to prevent any damage to the cupboard.

Assemble and Mount Under Sink Filter

Slide the filter cartridges inside the housings and tighten them using a housing wrench. Then, use a cordless drill machine to mount the under sink system as close to the cold water line as possible. Make sure you leave enough space beneath the housings so you can easily twist and remove them when needed.

If you don’t leave at least 4 inches of space, you’ll have trouble changing the filters later on.

Install Feed Valve

Remove the existing connector and fit in the adapter valve in the feed line. The adapter valve is usually a copper T that helps supply cold water to your existing faucet and under sink water filter simultaneously.

Drill a Hole

Here is the most tricky part! Drilling a hole in the countertop requires expertise and knowledge. The hole should neither be too big nor small for the new faucet. It is also important to align it with the old faucet, or the lack of symmetry will become a constant headache!

Select the drill bit depending on the material of your counter, i.e., granite, marble, lamination, etc.[1]

Another option is to use the pre-drilled hole on the sink for the soap dispenser.

Note: Please be warned that some people have damaged their countertops while attempting to drill a small hole. You might want to ask for help if you have no idea about drilling countertops.

Install Filtered Water Faucet

Slide the faucet in the new hole along with the washer. Don’t forget to use gaskets and putty underneath the washer to secure the hole completely.

Next, you might need a friend to help you. Tighten the fittings from underneath the sink as your friend holds the faucet from the top. Use washers, insert and brass fittings to make sure the connection is secure.

filling glass from filtered water dispenser

Establish Tubing Connections

Finally, it’s time to connect the filter system to the cold water line and the faucet. Measure the length of plastic tubing required and cut them to size using a tubing cutter.

Then connect the feed water to the inflow adapter valve on the filter system. Similarly, connect the outflow adapter valve to the filtered water faucet. Double-check all the connections to ensure they don’t pull out easily.

Turn On Water Supply

Gradually open the water supply to the unit to allow water inside the system.

Flush and Activate Filter Media

Open the dispenser and let the water run for a couple of minutes to flush the cartridges of your new under sink water filter and activate them.

Checking for Leaks

To avoid further trouble, inspect the filter system for leakages after one hour. If there’s a pool of water, tighten the connections and make other necessary changes.


In conclusion, you should prepare for an under sink water filter installation so you don’t end up having to make repeated visits to the local hardware store.

Some systems already include everything you need in the package, such as a T-valve, tubing and mounting screws.

Start the installation by turning off the water supply.

Remove the cold water line from under your kitchen sink and install the new feed valve.

Optionally, drill a hole in your countertop to install the filtered water dispenser.

Next, mount the under sink filtration system and establish all water connections.

Lastly, turn the water supply back on. Allow the new filters to flush while checking for leaks.

Further Reading


Meet Jason Hollow

Jason Hollow Jason is the founder of Water Masterz and head of content creation. After six years in the industry, he has tremendous knowledge and first-hand experience on all things related to water treatment.

His credo: Not a single American should have to drink unhealthy water at home.

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