Undersink Water Filter Air Purging Guide
Air bubbles in a newly installed or recently serviced undersink water filter are common. While the "milky" water or sputtering sounds might seem alarming, it’s usually just trapped air (oxygen) that needs to be purged.
Here is a step-by-step guide to getting your system running smoothly again.
1. Pre-Soak the Filters
Pre-soaking your filter cartridges before installation is the most effective way to prevent air from becoming trapped in the media blocks.
Fill a clean bucket or sink with clean water.
Submerge the new filter cartridges vertically.
Gently squeeze or tilt the filters under water to release trapped air bubbles.
Allow them to soak for 10 to 15 minutes before installing them.
2. Check for Visible Leaks
Before you start purging air, ensure the air isn't getting in through a loose connection.
Inspect the O-rings on the filter housings.
Check the Quick-Connect fittings (push-to-connect) to ensure the tubing is seated all the way in.
3. Flush the System (The Direct Method)
This is the most common fix. You need to force the air out by running a high volume of water through the lines.
Open the filtered water faucet completely.
Let the water run for 5 to 10 minutes.
You will likely hear "coughing" or sputtering noises; this is the air escaping.
Even if the sputtering stops, continue flushing to saturate the carbon blocks, which often hold tiny micro-bubbles.
4. The "Tilt and Shake" Technique
Sometimes air pockets get stuck in the "shoulders" of the filter canisters.
While the water is running at the faucet, gently tilt the filter unit or the individual canisters at a 45° angle.
Give the unit a very light shake.
Watch the faucet; you’ll likely see a sudden burst of bubbles or a "burp" of air.
Return the unit to its upright position and repeat if necessary.
5. Purge the Storage Tank (RO Systems Only)
If you have a Reverse Osmosis (RO) system, the air might be trapped in the pressurized tank.
Turn off the cold water supply valve to the system.
Open the RO faucet and drain the tank completely until the flow drops to a tiny trickle.
Close the faucet and turn the water supply back on.
Allow the tank to refill (usually 2–4 hours), then flush it one more time.
6. Check the Pre-Filter Housing
If the air persists after 24 hours, an air pocket might be trapped in the first stage housing.
Turn off the water supply.
Slightly unscrew the first filter housing (the one closest to the water inlet) just enough to break the seal.
Slowly turn the water supply back on until water begins to seep out of the top of the housing.
Immediately tighten the housing back up. This "bleeds" the air out of the top of the canister.
Additional Pro-Tips for Persistent Issues
Give it time: Micro-bubbles in carbon filters can take 48 to 72 hours of regular use to fully dissipate.
The Glass Test: Fill a clear glass with the "milky" water. If the water clears from the bottom up, it is definitely air. If it stays cloudy or settles at the bottom, you may have a sediment or filter quality issue.
Check incoming water pressure: Low or fluctuating water pressure can cause air locks to form and remain in the filter housing. Ensure your supply valve is fully open.
Inspect the O-ring lubrication: If an O-ring is dry, it can allow tiny amounts of air to be pulled into the system. Apply a food-grade silicone lubricant to the O-rings if you suspect a seal issue.
Here is a step-by-step guide to getting your system running smoothly again.
1. Pre-Soak the Filters
Pre-soaking your filter cartridges before installation is the most effective way to prevent air from becoming trapped in the media blocks.
Fill a clean bucket or sink with clean water.
Submerge the new filter cartridges vertically.
Gently squeeze or tilt the filters under water to release trapped air bubbles.
Allow them to soak for 10 to 15 minutes before installing them.
2. Check for Visible Leaks
Before you start purging air, ensure the air isn't getting in through a loose connection.
Inspect the O-rings on the filter housings.
Check the Quick-Connect fittings (push-to-connect) to ensure the tubing is seated all the way in.
3. Flush the System (The Direct Method)
This is the most common fix. You need to force the air out by running a high volume of water through the lines.
Open the filtered water faucet completely.
Let the water run for 5 to 10 minutes.
You will likely hear "coughing" or sputtering noises; this is the air escaping.
Even if the sputtering stops, continue flushing to saturate the carbon blocks, which often hold tiny micro-bubbles.
4. The "Tilt and Shake" Technique
Sometimes air pockets get stuck in the "shoulders" of the filter canisters.
While the water is running at the faucet, gently tilt the filter unit or the individual canisters at a 45° angle.
Give the unit a very light shake.
Watch the faucet; you’ll likely see a sudden burst of bubbles or a "burp" of air.
Return the unit to its upright position and repeat if necessary.
5. Purge the Storage Tank (RO Systems Only)
If you have a Reverse Osmosis (RO) system, the air might be trapped in the pressurized tank.
Turn off the cold water supply valve to the system.
Open the RO faucet and drain the tank completely until the flow drops to a tiny trickle.
Close the faucet and turn the water supply back on.
Allow the tank to refill (usually 2–4 hours), then flush it one more time.
6. Check the Pre-Filter Housing
If the air persists after 24 hours, an air pocket might be trapped in the first stage housing.
Turn off the water supply.
Slightly unscrew the first filter housing (the one closest to the water inlet) just enough to break the seal.
Slowly turn the water supply back on until water begins to seep out of the top of the housing.
Immediately tighten the housing back up. This "bleeds" the air out of the top of the canister.
Additional Pro-Tips for Persistent Issues
Give it time: Micro-bubbles in carbon filters can take 48 to 72 hours of regular use to fully dissipate.
The Glass Test: Fill a clear glass with the "milky" water. If the water clears from the bottom up, it is definitely air. If it stays cloudy or settles at the bottom, you may have a sediment or filter quality issue.
Check incoming water pressure: Low or fluctuating water pressure can cause air locks to form and remain in the filter housing. Ensure your supply valve is fully open.
Inspect the O-ring lubrication: If an O-ring is dry, it can allow tiny amounts of air to be pulled into the system. Apply a food-grade silicone lubricant to the O-rings if you suspect a seal issue.