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Home » Water Filtration Systems » Under Sink Water Filter Leaking (How to Fix It)

Under Sink Water Filter Leaking (How to Fix It)

By: Craig Smith
Published on:
Under Sink Water Filter Leaking- What to do?

If you come home to find your floors soaked and your chihuahua doggie paddling around the kitchen, you know there’s a problem. 

It’s possible your under-sink water filter is leaking. 

If so, you need to take care of it before the disaster spreads.

Under-sink water filters can operate for years without any trouble, but they can also spring leaks. A water leak could cause flooding and property damage, so if your under-sink water filter leaks, take care of it promptly.

You can usually fix a leaking under-sink filter yourself. This post explains what to do when your under-sink filter begins to leak. We discuss what the likely causes are and how to fix them.

How to Fix a Leaking Under Sink Water Filter

Below we go into the steps you need to take to determine why your under sink filter might be leaking and what you can do to solve this problem.

Troubleshooting Why Your Under-Sink Water Filter Is Leaking

The first step to fixing a leaking under-sink water filter system is figuring out why it’s leaking. Try to find the source of the leak. 

The most likely causes of leaks are:

  • Loose filter housing
  • Over tightened filter housing
  • Faulty o-ring
  • Clogged filter cartridge
  • Loose connection

Let’s go through these and discuss the signs that point to each issue and how to correct the problem. You should turn the water supply to the filter off before attempting any of these. 

Remember to relieve pressure in the system. Some systems have a pressure release button, but others do not. If there is no pressure relief, turn on the faucet coming from the filter for a couple of minutes to make sure there is no remaining pressure.

Loose Housing

The water filter housing is the part that holds your filter cartridges. Most look similar to this Hydronix housing below.


If you inspect everything and it appears water is leaking near the top of the filter housing, there is a good chance it is because the filter housing is loose. This is one of the most common causes of a leaking filter. If you suspect this is the case, follow these steps:

  1. Use your hands to verify one of your filter housings is loose. It should turn easily if it is too loose. 
  2. Once you’ve verified this is the problem, hand-tighten any loose filter housings.
  3. Use a water filter wrench to tighten the filter housings completely. These filter wrenches can be a strap wrench, like the one from Boeray(top), a plastic wrench, like the one from GE(middle), or a metal wrench, like the one from Superb Wrench(bottom). 



Avoid over-tightening housings so you don’t damage the entire unit.

Over-Tightened Filter Housing

This can also cause a slow leak near the top of the housing. An over-tightened housing could have damaged threads, flattened o-rings, or cracks. To fix this problem:

  1. Unscrew the housing from the system. 
  2. Inspect the threads on the housing and where it connects to the filtration system. Damaged threads could require a filter replacement.
  3. If you don’t find any damaged threads, check the o-ring. If it looks flattened or damaged then you’ll need to replace it. 
  4. Inspect the housing carefully for cracks, especially near the threads. Replace the housing if you find any cracks.
  5. Once you’ve verified there is no damage and replace the o-ring if necessary, reinstall the housing. Avoid over-tightening or you may damage the filter unit.

Faulty O-Ring

A bad o-ring can cause leaking near the top of the housing. 

The o-ring is the seal between your filter housing and the filtration unit. It should look like these iSpring replacements:


If you suspect this is your problem, follow these steps:

  1. Remove the housing.
  2. Examine the top of the o-ring for damage. If it appears flattened or shows signs of cracks, you’ll need to remove it from the housing.
  3. Install a new o-ring onto the housing.
  4. Reinstall the housing.

Clogged Filter Cartridges

If you have a leak from your filter housing and you suspect a clogged filter, follow these steps:

  1. Remove the housing.
  2. Install a new filter.
  3. Reinstall the housing.

Loose Connection

This can happen because of fluctuations in water pressure over time or because you jostled the water line or filter. If it appears one of your connections is loose, follow the steps below to correct it.

  1. Locate which line or adapter is loose.
  2. If it is a screw-on connection, carefully tighten it with a basic wrench. If it is a push-in or quick-connect connector, push the tubing firmly into the connection until you’re sure it is all the way in.

How To Change The Filter Cartridge And O-Rings

Cartridge replacement or replacement o-rings may be necessary if you have a clogged, damaged, or worn out filter. Filter replacements are part of the ongoing upkeep of your system as well. Here is the process: 

Turn Off The Water Supply

The first step is to shut off your drinking water supply. There may be a bypass valve near your under-sink water filter. If so, set it to “bypass” so you can work on your filter. 

If you don’t have a bypass, look under your sink for a shutoff valve for the cold water. This should be the same water line that feeds into your filter.

If you have no bypass and no shutoff under the sink, you may need to shut the water off where it enters your home. 

Release Pressure 

You need to release pressure inside your water filter before you open it up. Turn on the faucet running from your filter and let it drain all the water and pressure out. If your filter has a pressure release button, press it to release the rest of the builtup pressure.

Remove the Housing

Slide your water filter wrench over the housing and carefully remove  it. You may want to place a towel under the housing to catch any water spills.

Remove the Filter Cartridge

You should be able to remove the filter from the housing by just pulling it out by hand. If you have difficulty, you may need to use needle-nose pliers to grab onto it and pull it out.

Check the O-ring

Inspect the rubber o-ring for any signs of damage. Run your finger along it to feel any cracks or dips, and check to see if it looks flattened. If you find any damage, you need to replace the o-ring.

You can carefully pry it from its groove, then clean and dry the groove. Look for dirt or sediment buildup and remove that before installing a new one. 

The new seal should push into the groove. Be careful to make sure it is seated properly into the groove.

Clean the Housing

Use soapy water to give the housing a good wash. Make sure to remove all sediment and dirt from the housing.

Install the New Filter

Slide the new filter cartridge down into the housing. Make sure to seat it properly into the groove at the bottom if your housing has one.

Reinstall the Housing

Place your housing back onto the system and tighten it by hand. You can then snug it up a bit more using a wrench designed for under-sink water filters, but don’t over-tighten it or you may damage the system.

Turn on the Water

At this point, turn your water supply on. Run your faucets for at least five minutes to flush the new water filters. Then check for leaks under your sink, especially around your water filter. 

What to Do After Fixing the Leak

Once you’ve finished repairing the leak and reassembling everything, turn the water back on. Make sure to turn it on slowly so you don’t cause damage from a sudden water pressure surge. 

Any time you replace water filters or open your filtration system to work on it, you should run water for about five minutes to flush the system. 

Carefully inspect around your filter to verify you’ve taken care of all of the leaks.

In Conclusion

A leaking under-sink water filter isn’t fun, but it’s no reason to panic. By following the guide above, you can fix the leak yourself in most cases. This saves the expense of hiring a professional plumber, and it also takes care of the issue before any more damage can occur.

If you don’t want to deal with the repair then you can always buy a new under sink water filter also. 

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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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