RO filter maintenance is four jobs on two different clocks. The prefilters and the polishing carbon run on a calendar because they are protecting the membrane and the taste. The membrane itself runs on performance, and replacing it early wastes money while replacing it late quietly costs you the treatment you thought you were getting.
The parts that wear, in order
The sediment prefilter takes the grit and is the stage that blinds first, showing up as a slow refill. The carbon prefilter strips chlorine before it reaches the membrane, and its failure is invisible because a chlorine breakthrough damages the membrane without any symptom you can taste. The membrane rejects dissolved solids and degrades gradually. The postfilter carbon polishes tank water on the way to the faucet and is what stops stored water tasting flat. The tank bladder is the fifth item people forget, and it fails as apparent loss of capacity.
A schedule you will actually keep
Change both prefilters together, on the manufacturer interval, adjusted shorter if your feed water is sedimented or heavily chlorinated. Change the postfilter at the same time or every second time. Leave the membrane alone until performance says otherwise, which is usually several years on protected water. Write the date on the housing with a marker at every change, because nobody remembers, and set a calendar reminder that repeats. The commonest failure of a reverse osmosis system is not a broken part, it is a household that stopped changing cartridges three years ago.
Measure rather than guess
A handheld total dissolved solids meter turns membrane maintenance from a guess into a number. Take a reading of the feed water and a reading at the reverse osmosis faucet, and note the difference when the system is new and healthy. Repeat every few months. When the gap between them has narrowed substantially against that baseline, the membrane is passing what it used to reject and it is time to replace it. Fill time is the other measurement worth taking: a tank that takes far longer to fill than it did points at prefilters, low pressure or a tired membrane.
Sanitizing and putting it back together
Sanitize when you open the system for a membrane change, after any long period standing unused, and after work on the plumbing. Shut the feed, drain the tank, remove the cartridges and membrane, add the sanitizer the manufacturer specifies to the first housing, reassemble empty, let the system fill and stand for the stated time, then flush the tank fully several times before drinking. On reassembly, lubricate and seat the o rings properly, hand tighten housings with the supplied wrench rather than overtightening, and dry the joints and check them again the next morning.
Questions people ask about ro filter maintenance
How often should reverse osmosis filters be changed?
Sediment and carbon prefilters on the manufacturer interval, shorter on sedimented or heavily chlorinated water. The membrane is replaced on measured performance rather than on a calendar.
How do I know the membrane needs replacing?
Compare a total dissolved solids reading of the feed water with one at the reverse osmosis faucet against the baseline you took when it was new. A narrowing gap means the membrane is passing more through.
Why is my reverse osmosis tank filling so slowly?
Usually blinded prefilters, low feed pressure or a tank that has lost its air charge. Check the cheapest of those first by changing the sediment prefilter and noting whether fill time improves.
Do I need to sanitize a reverse osmosis system?
Yes, when you open it for a membrane change, after standing unused for a long period, or after plumbing work. Flush the tank thoroughly afterwards before drinking the water.