Filter life varies by an order of magnitude across the formats a household might own, and the reason is simply how much media each contains against how much water passes through it. Knowing the pattern makes the running cost of each format obvious and explains why the small convenient ones are the expensive ones per volume treated.
The small formats
A pitcher cartridge holds very little media and is rated in a modest number of gallons, so a household drinking steadily replaces it every month or two. A tap mounted filter is similar and runs down faster still if the diverter is left on filtered for washing up, which is why that habit matters. A refrigerator cartridge is typically rated for six months, though an ice maker refilling through the day consumes it whether or not anyone uses the dispenser.
The plumbed formats
An under sink cartridge holds considerably more media, so intervals are typically six months to a year depending on the format and the water. A whole house sediment cartridge is judged by pressure drop and can run anywhere from weeks on a dirty well to most of a year on a clean supply. A whole house carbon cartridge runs on volume, usually six months to a year. A backwashing media bed lasts years, because there is far more media and it is cleaned rather than replaced.
Membranes and specialist media
A reverse osmosis membrane lasts several years when its prefilters are maintained, and is replaced on measurement rather than a calendar: compare dissolved solids in the feed against the product taken before the tank. Softener resin lasts many years unless fouled by iron or degraded by chlorine. Remineralization media is consumed silently and goes on the annual schedule. Ultraviolet lamps are the exception to everything here: annually, regardless of use or appearance.
What shortens every one of them
Missing or blocked sediment prefiltration, since particles blind carbon surfaces and abrade membranes. A chloraminated supply where the media was specified for free chlorine. Higher household use than the rating assumed. Standing unused, which lets growth establish in wet media. And filtering water nobody drinks, which is the easiest thing to fix: use the diverter. Our replacement filter guide covers matching cartridges and keeping a schedule that survives a busy year.
Questions people ask about how long do water filters last
Which format lasts longest?
A backwashing media bed, measured in years, because it holds far more media and is cleaned rather than replaced.
Why do pitcher and tap filters run out so fast?
They hold very little media, and tap filters run down faster still if filtered water is used for washing up.
How is a membrane's life judged?
By measurement, comparing dissolved solids in the feed against the product before the tank, not by a calendar.
What shortens filter life most?
Missing sediment prefiltration, a chloraminated supply the media was not specified for, and filtering water nobody drinks.