How to Change Water Filter Cartridges
Updated February 20, 2026
Swap out sediment, carbon, and specialty cartridges in whole-house and under-sink systems -- the right filters, the right schedule, and the correct order for multi-stage setups.
Overview
Here is what most people do not realize about water filters: an overdue filter does not just stop working -- it can actually release trapped contaminants back into the water as flow forces them through the saturated media. That means your water quality can be worse than if you had no filter at all. Sediment filters clog, carbon filters max out, and specialty filters exhaust their treatment media. Standard cartridges need swapping every 3-6 months, specialty ones every 6-12 months, though the actual timing depends on your water quality and how much water you run through the system. The swap itself is straightforward: shut off the water, unscrew the housing, pull the old cartridge, drop in the new one, and flush.
What You'll Need
Safety First
- Shut the water off before you touch the housing. Whole-house systems: close the valves on both sides of the filter (or shut off the main). Under-sink systems: close the cold water valve under the sink. Then open a faucet downstream to bleed off the pressure.
- The filter housing is full of water and under line pressure. Put a bucket underneath before you unscrew it -- 1-3 quarts will pour out. If the housing is stuck tight, make sure you actually released the pressure by opening a downstream faucet. Trying to unscrew a pressurized housing is a recipe for a mess.
Step-by-Step Instructions
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Identify Your Filter Type and Get the Correct Replacement
Before you buy anything, figure out exactly which cartridge your system uses. Filters vary by size (standard 10-inch, big blue 20-inch, slim-line), type (sediment, carbon block, granular activated carbon, specialty media), and micron rating (lower number = finer filtration). Look for a model or part number printed on the end cap of the existing filter, and check the housing for the manufacturer name. If you cannot find any markings, measure the cartridge: standard residential is 2.5 inches diameter by 10 inches long, big blue is 4.5 inches by 10 or 20 inches. Get the exact match -- a wrong-size cartridge will not seal right and unfiltered water will bypass it entirely.
Tip: Snap a photo of the old filter or bring it to the hardware store. A lot of systems use proprietary cartridges that look almost identical to standard sizes but have slightly different dimensions or O-ring setups. Close enough does not cut it here -- a wrong fit causes bypass leaks. -
Shut Off Water and Depressurize the System
Whole-house: close the inlet valve before the filter housing. If there is an outlet valve too, close that as well. Open the nearest downstream faucet to bleed pressure. Under-sink: close the cold water valve and open the filtered water faucet if the system has a dedicated one. Either way, put a bucket underneath and give it 30 seconds for the pressure to equalize before you start unscrewing anything.
Tip: No shut-off valves on your whole-house filter? That means you have to kill the main water supply every time you change filters. Having a plumber add ball valves on both sides ($50-100) is one of those upgrades that pays for itself fast in convenience. -
Remove the Filter Housing and Old Cartridge
Grab the filter wrench (the large plastic strap wrench that came with the system, or a universal one from the hardware store for $8-12) and unscrew the housing counterclockwise. Keep it upright until you can pour the water into the bucket. Pull the old cartridge out. Take a look inside the housing -- if it is gunked up with sediment, slime, or discoloration, wash it out with warm soapy water and rinse well. Check the O-ring at the top where the housing seals against the filter head. If it is cracked, flat, or missing, replace it ($2-5, specific to your housing model). Either way, put a thin coat of food-grade silicone grease on the O-ring -- it helps it seal and makes the next filter change easier.
Tip: Do not skip the wrench. These housings tighten under water pressure and after a few months they are basically welded on. If you lost the original wrench, universal ones are $8-12 at any hardware store. Do not try pliers or a pipe wrench -- you will crack the plastic housing. -
Install the New Cartridge and Reassemble
Drop the new cartridge into the housing. Most have an open end and a closed end -- they only fit one way, with the open end facing up toward the filter head. Multi-stage system? Install in the correct order: stage 1 is usually a sediment pre-filter (5-20 micron), stage 2 is a carbon block (1-5 micron), and stage 3 is a specialty filter for things like lead, iron, or fluoride. The stages are typically numbered on the housing or in the manual. Screw the housing back on, hand-tighten firmly, then give it a quarter turn with the wrench. Stop there -- the O-ring makes the seal, not force.
Tip: Multi-stage setup? Replace all cartridges at the same time even if the lifespans are different. It keeps your filtration consistent and simplifies the schedule. The cost difference between changing one filter and all three is usually $15-30 -- worth it for the simplicity. -
Flush the System and Check for Leaks
Turn the water back on slowly and check for leaks at the seam where the housing meets the filter head and around the O-ring area. Dripping? Shut off the water, reseat the O-ring, and snug it up again. Once it is dry, flush the system by running water through the filtered faucet for 5-10 minutes. New carbon filters put out grey water or black carbon fines at first -- totally normal and harmless. Keep flushing until it runs clear. For whole-house systems, run a bathtub faucet for faster flow. When you are done, write the date on the housing with a marker or set a phone reminder for the next change.
Tip: Some carbon filters have a slight taste for the first few gallons. If it tastes off after the initial flush, run another 5 gallons through. If the taste persists beyond 10-15 gallons, the cartridge may be defective or the wrong type -- contact the manufacturer.
Pro Tips
- Set a recurring phone reminder: every 3 months for sediment and carbon, every 6 months for specialty filters, every 12 months for RO membranes. Forgetting to change filters is the number one reason home filtration systems stop doing their job.
- Buy in bulk. Most manufacturers sell 3-packs or 6-packs at a solid discount. A full year of filters costs less than one service call from a water treatment company.
- If your sediment filter clogs way ahead of schedule -- like monthly instead of every 3 months -- your source water has high sediment. Add a spin-down sediment filter ($30-50) ahead of the cartridge filter. Spin-downs catch the big stuff and you clean them by opening a flush valve instead of replacing a cartridge. Your cartridge filters will last much longer.
- Do not try to wash and reuse standard filter cartridges. The media is single-use -- washing a sediment filter removes visible particles but does not restore its filtration capacity. The only exception is pleated sediment filters specifically labeled as washable.
- On well water? Test annually and match your filter stages to whatever contaminants show up. A generic sediment-plus-carbon setup might miss the things that actually matter in your water -- iron, manganese, hydrogen sulfide, bacteria. Our water quality testing guide covers this in detail.
When to Call a Pro
You do not need a pro to change filter cartridges. But call a water treatment specialist if you are not sure which cartridges fit your system, if the housing itself is cracked or leaking from the body (not just the O-ring), if you want to upgrade to a better filtration setup, or if you are on well water and need a customized plan based on a water test.