How often should you change a whole-house water filter?

Short answer

Change the whole-house water filter every 3 to 6 months for a sediment filter, up to 12 months for a carbon filter. The filter sits in a canister on the main water line, usually near where it enters the house, and everything the house uses passes through it. On well water with a lot of sediment, change the sediment cartridge every month. A swap takes 15 to 20 minutes and a cartridge costs $15 to $60.

Why it matters

A sediment filter is a strainer. Sand, rust and grit that would otherwise reach every faucet, valve and appliance get caught in its pleats. A carbon filter goes further and pulls out chlorine, odors and some chemicals. Both have a limit, and both work the same way when they reach it: the water keeps coming, just more slowly and less clean.

The first thing you notice is pressure. A loaded cartridge chokes the whole house, so the shower weakens and the washing machine takes longer to fill. What you don't see is worse. A sediment filter left in too long lets fine particles through to the water heater, the ice maker and the valves in every fixture. A carbon filter that's been wet for a year grows bacteria on the organic matter it caught, and a cartridge that was meant to clean the water starts seeding it. Changing on schedule keeps the filter doing the job it was installed for instead of becoming the problem.

When to do it more often

Well water with a lot of sediment: change the sediment cartridge every month. Some wells throw enough sand to load a cartridge in weeks, and a pressure gauge on the housing tells you when.
A household that uses a lot of water: everything the house uses goes through the filter, so a big family loads it faster than a couple does.
After work on the water main or the well: a burst of sediment follows, and a fresh cartridge afterward is cheaper than finding grit in every faucet.

What you need

The filter housing wrench, the big plastic ring that came with the housing and fits around the canister
A bucket, since the canister is full of water when it comes off
A replacement cartridge of the same size and type
Silicone grease for the o-ring, a little dab that keeps the seal from leaking

Steps at a glance

Close the valve before the filter, and the valve after it if there is one, then open a tap in the house to drop the pressure.
Press the red button on top of the housing if it has one, to release the pressure in the canister.
Fit the wrench around the canister and turn it to unscrew, with the bucket underneath.
Lift out the old cartridge and rinse the canister.
Check the o-ring, wipe it, and put a thin coat of silicone grease on it.
Drop in the new cartridge, screw the canister back on hand tight, and snug it with the wrench.
Open the valves slowly, press the button again to bleed air, and check for drips.

You're done when the canister is dry on the outside, the tap runs at full pressure, and the water runs clear.

Signs it's overdue

A drop in water pressure through the whole house, at every tap at once.
A cartridge that's brown or gray when you look through a clear housing.
A change in the water's taste, back toward chlorine or the well's own flavor.
The date on the housing has passed.

DIY or pro

This is an easy job once you've done it the first time. The housing wrench and the pressure button are what make it go smoothly, and the only way to go wrong is to skip releasing the pressure before unscrewing, which sends water everywhere. A canister that won't unscrew by hand usually needs a longer lever on the wrench, not more force on the housing.

A plumber charges $100 to $200 to change a cartridge, which makes sense if the housing is cracked or leaking and needs replacing at the same time, or the shut-off valves around it are stuck. Otherwise, keep a spare cartridge on the shelf and do it yourself.

Safety

Pressure: the canister holds water at full house pressure. Close the valve ahead of it and release the pressure before you turn the wrench, or the canister can come loose with force and spray. Open the valves slowly afterward so the housing fills without a shock.

FAQ

How do I know when to change a whole-house water filter?

Pressure drops through the whole house at once. If the housing is clear, a dark cartridge is the sign. Otherwise go by the schedule: every 3 to 6 months for sediment, up to 12 months for carbon.

What happens if you don't change the whole-house filter?

The pressure drops, sediment gets through to the appliances, and a carbon filter left wet for too long can grow bacteria.

Can I clean and reuse a whole-house filter cartridge?

Only a washable mesh or pleated cartridge sold as reusable. Standard sediment and carbon cartridges are replaced.

Do I need both a sediment and a carbon filter?

Sediment first, to take the grit out, and carbon after it if you want chlorine and odors removed. On city water, carbon alone is often enough. On a well, sediment is the one that matters.