How to Replace an Under Sink Water Filter Cartridge

Author: Jason Hollow - Published: 2021/09/22 - Updated: 2023/01/05

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Maintaining your under sink water filter is a simple task that involves periodic cartridge replacements and occasional cleaning. Most homeowners choose to replace their filters and sanitize their system themselves, while others hire professional services.

If you belong to the former group, we advise you to learn the basics of the process. Failure to replace filter cartridges accurately will not only lead to leakages, but you might end up spending more on costly repairs later on.

So, here is a comprehensive step-by-step guide on how to change your under sink water filter cartridge easily and quickly!


  1. First, close the water supply valve.
  2. Open the sink faucet to release pressure.
  3. Remove filter housing.
  4. Inspect (and replace) O-rings.
  5. Sanitize and clean filter housing.
  6. Install the new filter cartridge.
  7. Reinstall filter housing.
  8. Open the water supply while checking for leaks.

How to Replace an Under Sink Water Filter – Guide

How to Change an Under Sink Water Filter Thumbnail

Before we move on to how you can replace an under sink water filter without breaking anything, it’s crucial to figure out the ideal time for it.

Water filters come with clear instructions regarding how frequently they should be replaced. However, the service life of your filter cartridge will vary according to the quality of the source water and everyday usage. In short, you might need to change your cartridges more or less often than your neighbor who uses the same filter.

So, what are the tell-tale signs? Most importantly, look out for pressure drops. If the water pressure is down, it’s likely your under sink filter is clogged. Secondly, always keep a log of your filter replacements and ensure you stick to it religiously.

With that said, let’s move on to the task on hand.

Collect Your Supplies

Most under sink filtration systems are designed to facilitate quick and tool-free replacements. Therefore, all you need are a few basic supplies that are probably lying around your house. The process usually takes less than half an hour if you have all the tools at hand. You will need:

  • A basic housing wrench (made of plastic or metal),
  • A torchlight if the cabinet under your sink is dark,
  • And, of course, replacement filter cartridges of the correct size.
  • You might also need a few spare O-rings of the desired size which are usually included with a new filter cartridge.

If it’s your first time, we advise asking a friend or partner to help you. Now, roll up your sleeves and get ready to plunge in.

Turn Off Water Supply

Before you attempt to change the filters, turn off the incoming water supply, or you’ll end up flooding your kitchen. Don’t know how?

Most under sink water filters are equipped with a bypass valve right next to the inflow valve. Turn it on to bypass the unit and stop the water supply.

If you don’t see a bypass valve, locate the cold water valve towards the back of the kitchen sink cabinet and turn it off.

If the cold water valve is stuck or faulty, you will have to turn off the main feed water valve. You will find it at the point where water enters your house. But remember to turn off all water-using appliances and inform the family members since the water supply to the whole house will be cut off.

Depressurize the Unit

Next, you must depressurize the unit by removing all remaining water and air from it. Turn on the filtered water dispenser and let the water run out. Simultaneously, press and hold the pressure release buttons on the system.

You will find it easier to remove the housings of your under sink water filter when they are deflated.

Remove Filter Housings

Loosen filter housings either using your hands or a filter wrench. If it’s stuck due to over-tightening or cross-threading, you will find it helpful to use a piece of flannel for better grip.

Slide the wrench from the bottom over the filter housing. Twist it towards the left, and then use your hands to remove the housing altogether. Oftentimes there is residual water in the sump that needs to be drained in the sink.

If the under sink filter housing is badly stuck, try using a sturdy metal housing wrench. Some people also swear by using a strap wrench to remove jammed sumps.

It helps to remember that all housings should not be removed at the same time. This practice prevents confusion and mess.

Remove and Inspect the Filter Cartridges

Next, slide out the first filter cartridge using your fingers or a pair of nose pliers. Examine it closely to see whether it has completed its life or is chock-full of gunk.

You see, you should not be replacing filter cartridges too soon or too late. Checking the cartridge will give you an idea about when it should be replaced the next time around.

Replacing it too soon means you end up wasting money. Similarly, replacing cartridges too late will compromise the water quality your under sink water filter system produces.

Most carbon filters have two O-rings on either side to ensure they sit perfectly inside the filter housing. Sometimes the O-rings get stuck to the bottom of the sump. It’s necessary to remove all old O-rings too to make room for the new ones.

Change or Clean the O-ring

Remove the O-ring seated in the channel under the threads of the canister. Carefully inspect the O-ring for any signs of damage. It must be replaced if it’s broken, inflexible, crushed or has scratches all over.

If the O-ring is in good shape, lubricate it using silicone grease. Lubricating the rubber gasket ensures it remains functional for a long time.

Clean the Filter Housings

Most people assume that their under counter filtration systems don’t require cleaning. Well, it couldn’t be further from the truth. Ideally, filter housings must be cleaned at every cartridge replacement.

Dirt or sediment can quickly start to build up inside the housings. Moreover, plastic canisters attract mold and mildew growth. Hence, it’s best practice to spend an extra ten minutes to ensure your filtration system is free from germs and buildup.

Avoid using harsh chemicals to clean your filter housings, though. Make a solution of liquid soap and water and pour it into each container. Then, use a long brush to clean the interior of the sump.

Don’t forget to clean the O-ring channel as well, using a small brush. Finally, rinse the housing properly and allow it to air dry.

Sanitize the System (Biannually)

You may need to sanitize your under sink water filter about twice a year to prevent the growth of bacteria and algae. Prepare a diluted sanitizing solution using household bleach or use an NSF-certified sanitizing liquid.[1]

Next, screw the empty filter housings back on the sump and turn on the water supply to the filtration system. Open the cold water faucet for a few seconds, so the sanitizing solution reaches all the lines and the dispenser.

Let the unit soak for thirty minutes. Then turn on the faucet to drain the solution. Finally, let the system flush for a few minutes to ensure the bleach has rinsed out thoroughly.

Turn off the water supply and remove the filter housings again.

Install New Cartridges

two water filter cartridges dropped in water

Simply slide the new filter cartridges inside the containers.

Screw the Housings on the Cap

Reassemble the unit carefully. First, use your hand to twist the filter housings back to the cap. Then, tighten them using your filter wrench. Remember, don’t overtighten, or you’ll end up cracking one or more components.

Turn on the Water Supply

Gradually turn on the water supply. This is important because a sudden surge in the water pipes can damage your under sink water filter. Turn on the faucet and allow the water to run for five minutes to flush and activate the new filter cartridges.

Inspect the system after a few hours to ensure there are no leaks. Congratulations, you’re all done!

Tips: What Else to Consider

  • Don’t over-tighten or under-tighten the housings.
  • Replace O-rings at every filter change to ensure your system doesn’t leak.
  • Use a metal water filter wrench or a strap wrench to deal with hard-to-remove housings.
  • For under sink reverse osmosis systems: When you empty the unit for cartridge replacements, use the opportunity to check the RO tank pressure. Generally, reverse osmosis storage tanks should be re-pressurized at least once a year to about 6-8 psi.


In conclusion, replacing an under sink water filter doesn’t need to be complicated.

As soon as one or more filter elements have exceeded their lifespan, collect your supplies and get ready.

Start by turning off the feed water and depressurize the system.

Remove all filter cartridges and check their condition.

Clean the filter housings and check any O-rings.

Install new filters were needed and put everything back together before turning on the water supply.

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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