Under sink filter replacement, step by step

Advertised prices, verified

How to replace an under sink filter

1. Shut off and depressurize. Close the feed valve on the cold line under the sink, then open the filtered-water faucet until flow stops. Skipping the depressurize step is how cabinets get soaked, because the housing is still holding line pressure when you crack it open.
2. Swap the cartridges. Twist-lock heads release with a quarter turn; sump-style housings need the wrench that came with the system. Wipe the housing interior, check the o-ring for cracks and seat the new cartridge without forcing it. A stubborn housing usually means pressure was not fully relieved.
3. Flush before drinking. Open the feed valve slowly, check every joint for weeping, then run the faucet for the flush period the cartridge maker specifies. New carbon sheds harmless black fines at first, and the flush clears them along with any preservative the media shipped with.
4. Date the housing and reorder. Write the change date on the housing and put the next set of cartridges in the cabinet now. Under sink filters fail quietly by exhaustion rather than loudly by leaking, so the written date is the only honest reminder you will get.

Replace the cartridge or replace the system

A sound housing with available cartridges is worth keeping: the housing is plumbing, and plumbing does not wear out on a cartridge schedule. Replace the whole system when the o-ring groove is worn and will not seal, when the maker has discontinued the cartridge so every change becomes a compatibility hunt, or when your water problem has changed and the old media no longer targets it.

The comparison is straightforward with the table above: several years of cartridge sets for the old unit against the price of a current system that includes its first set. If the old system uses proprietary cartridges priced near what a whole new standard-housing system costs, switching to standard housings pays for itself quickly and every future replacement gets cheaper.

What an under sink filter cannot fix

An under sink unit treats one faucet, so scale in the water heater, iron stains in the tub and chlorine in the shower are untouched by it. If the complaint list is longer than taste and clarity at the kitchen sink, price a whole-house system instead, and if you are on a well, run a proper test first: our well water testing guide covers what to check before buying any point-of-use equipment.

Common questions

How long does an under sink filter replacement take?

Budget under an hour for a routine cartridge swap including the flush, and longer the first time while you find the shut-off and learn the housing. No special tools are needed beyond the housing wrench supplied with sump-style systems.

Why is water dripping after I replaced the under sink filter?

Almost always the o-ring: it is pinched, dry or seated in a dirty groove. Depressurize, remove the housing, clean the groove, lubricate the ring with food-grade silicone grease and reseat it. Overtightening the housing causes leaks as often as it cures them.

Do I need a plumber for under sink filter replacement?

Cartridge changes are homeowner work. Call a plumber only if the shut-off valve under the sink is seized or the system is being replaced with one that needs a new tee, drain connection or dedicated faucet hole.

What does under sink filter replacement cost per year?

It depends on how many stages your system runs and whether the cartridges are standard or proprietary. The table above shows current vendor pricing, with $1,531 as the midpoint across the sets we track.

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