The filters for reverse osmosis systems are the consumable cartridges around the membrane, not the membrane itself. A typical unit carries a sediment cartridge, one or two carbon blocks before the membrane, and a polishing carbon filter after the storage tank, and each has a different job and a different service life.
Stage one: sediment
The first cartridge takes out sand, rust, silt and pipe scale so that none of it reaches the carbon or the membrane face. On city water it is usually a melt-blown polypropylene cartridge that lasts about a year. On a well or after utility mains work it loads far faster, and a cartridge that comes out orange is telling you there is untreated iron upstream. This is the cheapest cartridge in the set and the one whose neglect costs the most, because everything behind it clogs when it fails.
Stage two: carbon before the membrane
The carbon block adsorbs chlorine, which chemically attacks thin-film composite membranes, along with taste and odor compounds. Its exhaustion is invisible, so it is replaced on schedule rather than on appearance. Supplies disinfected with chloramine need catalytic carbon, because standard activated carbon removes chloramine far more slowly and lets it through to the membrane. Some systems run two carbon stages in series, which extends protection but does not remove the need to change them on time.
Stage four: the polishing filter
After the storage tank sits an inline carbon filter, usually changed annually. Water sitting in a bladder tank picks up a flat, faintly rubbery taste, and this last stage takes it off on the way to the faucet. It is the cheapest cartridge to change and the one whose neglect you actually taste, so if a system's water has gone dull while everything else seems normal, this is the first thing to swap. Change it after the tank has been sanitized as well, not before.
Building a schedule that fits your water
Annual on the prefilters and the polishing filter is the sensible default for city water, with the membrane replaced when a total dissolved solids reading shows rejection has slipped. Well water, high sediment and heavy household use all shorten the prefilter interval. Set a recurring reminder rather than waiting for a symptom, since by the time taste returns the membrane has already been exposed. Our reverse osmosis replacement filters guide covers matching cartridge sizes and standards to your housing.
Questions people ask about filters for reverse osmosis
Do all the filters get changed at the same time?
Prefilters and the polishing filter are usually changed together annually. The membrane lasts much longer and is replaced only when its rejection rate falls off.
Can I use generic cartridges in a branded reverse osmosis system?
If it takes standard ten-inch cartridges, yes, and it usually costs less. Proprietary quick-change designs accept only the maker's own cartridges.
What happens if I skip a carbon prefilter change?
Chlorine reaches the membrane and permanently degrades it. You lose an expensive membrane to save a cheap cartridge, and the loss shows up as poor rejection, not a leak.