Turn off the water supply before you open the filter housing

The first step is to shut off the water at the main valve or at the shut-off valve closest to your filter system. This stops water pressure from building up inside the housing and prevents water from spraying out when you open it. Most shut-off valves are located under the sink, on the wall near your water heater, or at the point where the main line enters your home.

Turn the valve clockwise until it stops. You do not need to force it—hand-tight is enough. If you cannot find a shut-off valve near the filter, or if it will not turn, you may need to shut off water at the main meter outside your home. Once the valve is closed, open a nearby faucet to release any remaining pressure in the line.

Key Takeaways

  • Always shut off the water supply before opening the filter housing to prevent water from spraying and to make the cartridge easier to remove.
  • Most cartridges twist out by hand or with a filter wrench, and you should replace the rubber seals (O-rings) at the same time you replace the cartridge.
  • Rinse the new cartridge with cold water before installing it to remove loose carbon dust and set up the filter media.
  • After installation, turn the water back on slowly and check for leaks around the housing cap before using the filtered water.
  • The timing for replacement depends on your water quality and daily use, but most cartridges last between three and six months.

Open the filter housing and remove the old cartridge

Once the water is off, locate the filter housing—the cylindrical or canister-shaped container that holds the cartridge. Most under-sink filters have a housing that screws onto the top of the unit. Use a filter wrench (a specialized tool that grips the housing cap) or an adjustable wrench to turn the housing counterclockwise. If you do not have a wrench, you can wrap a rubber band around the cap to improve grip and turn it by hand.

As the cap loosens, water may drip out. Have a towel or bucket ready. Once the cap is off, you will see the cartridge inside. It usually looks like a white or tan cylinder. Grip it firmly and twist it counterclockwise to unscrew it from the base, or pull it straight out if it slides in without threading. Some cartridges are held in place by a clip or bracket—check your filter's manual if the cartridge does not come free easily.

Inspect and replace the rubber seals

Before you install the new cartridge, look at the rubber O-rings (seals) inside the housing cap and at the base where the cartridge screws in. These rings prevent water from leaking around the cartridge. If they look cracked, flattened, or discolored, they should be replaced. Many filter kits include new O-rings, or you can order them from the filter manufacturer using your model number.

Remove the old O-ring by gently prying it out with your fingernail or a plastic tool. Do not use a sharp metal object, which can scratch the groove it sits in. Clean the groove with a dry cloth, then slide the new O-ring into place. Make sure it sits evenly all the way around—a twisted or bunched O-ring will cause leaks. explore a thin coat of food-grade silicone grease to the new O-ring so it seats properly and does not dry out.

Rinse and install the new cartridge

Remove the new cartridge from its packaging and rinse it under cold running water for 10 to 15 seconds. This removes loose carbon dust and activates the filter media. Do not use hot water, which can damage some filter materials. Hold the cartridge upright and let water run over the pleated surface until the water runs clear.

Insert the cartridge into the housing base and twist it clockwise by hand until it is snug. Do not over-tighten—you should be able to turn it with firm hand pressure, not a wrench. If your cartridge slides in without threading, push it straight in until you hear or feel it click into place. Screw the housing cap back onto the base, turning it clockwise with your wrench or by hand until it is hand-tight. Again, do not over-tighten, which can crack the cap or damage the O-ring.

Turn the water back on and check for leaks

Slowly turn the shut-off valve counterclockwise to restore water pressure. Open it gradually over 10 to 15 seconds rather than all at once—this prevents a sudden pressure surge that can damage the new cartridge or dislodge the O-rings. Once the valve is fully open, turn on a nearby faucet and let water run for 30 seconds to flush air from the line.

Watch the filter housing for drips or streams of water. A small drip at the base of the cap during the first minute is normal as the O-ring settles, but steady leaking means the cap is not seated properly or the O-ring is twisted. If you see a leak, turn the water off, remove the cap, and check that the O-ring is seated evenly and the cartridge is fully inserted. Tighten the cap slightly and try again. Do not use the filtered water until the leak stops.

Know when to replace your cartridge

Most water filter cartridges last between three and six months under normal household use, though this varies based on your water quality and how much water you use daily. If your water is very hard or contains sediment, the cartridge will clog faster. Some filters have a change indicator—a valve that clicks or changes color when the cartridge is saturated—so you do not have to guess.

If you notice the water pressure dropping, the filtered water tastes or smells off, or the cartridge looks visibly discolored or clogged, it is time to replace it. Waiting too long reduces the filter's effectiveness and can allow bacteria to grow inside a saturated cartridge. Mark your calendar three months after installation as a reminder to check the cartridge, and keep a spare on hand so you are not without filtered water while waiting for a replacement to arrive.

Common mistakes to avoid

Do not skip the step of turning off the water. Trying to change a cartridge under pressure is messy, makes it harder to remove the old one, and risks damaging the O-rings. Do not over-tighten the housing cap or the cartridge itself—hand-tight is correct, and over-tightening can crack plastic parts or pinch the O-ring, causing leaks.

Do not install a new cartridge without rinsing it first. Carbon dust from manufacturing can discolor your water for the first few uses. Do not ignore leaks after installation—they mean the seal is not working, and water is bypassing the filter. Finally, do not assume all cartridges fit all housings. Check your filter's model number and buy the exact cartridge it calls for, as sizes and threading vary widely.

Frequently Asked Questions

Can I reuse a water filter cartridge?

No. Once a cartridge is saturated, it cannot be cleaned or recharged. Attempting to reuse it wastes water and does not filter effectively. Some cartridges can be recycled through the manufacturer or a local waste program—check the packaging or the manufacturer's website for instructions.

What if the old cartridge is stuck and will not twist out?

Use a filter wrench with a firm grip and turn slowly rather than yanking. If it still will not budge, wrap a rubber band around it for extra grip, or soak the base with a damp cloth for a few minutes to soften any mineral buildup. If the cartridge is cracked or broken, you may need to call a plumber to remove it safely without damaging the housing.

Do I need to flush the system after changing the cartridge?

Yes. Run water through the filter for 30 seconds to one minute after installation to remove air and carbon dust. Some filters recommend flushing for longer—check your manual. The water may look slightly discolored or taste like carbon for the first few uses; this is normal and harmless.

How do I know which cartridge to buy?

Look at your filter housing or the manual for the model number, then search for that number plus "replacement cartridge." Cartridges are not universal—a cartridge for one brand or model will not fit another. Buying the wrong size wastes money and leaves you without filtered water.

What should I do if water leaks after I install the new cartridge?

Turn off the water, remove the cap, and check that the O-ring is seated evenly in its groove and not twisted. Make sure the cartridge is fully inserted and the cap is hand-tight, not over-tightened. Reinstall and test again. If leaking continues, the O-ring may be damaged and need replacement.