How often should you change reverse osmosis filters?
Updated July 2026
Swap a reverse osmosis system's sediment and carbon pre-filters every 6 to 12 months, change the carbon post-filter yearly, and replace the RO membrane every 2 to 3 years. The order matters: the cheap pre-filters exist to protect the expensive membrane, catching grit that would tear it and chlorine that would chemically destroy it. Ride them too long and you sacrifice a $50-90 membrane to save a $30-70 set of filters, which is the opposite of the point. A basic TDS meter is the tiebreaker that tells you when the membrane is genuinely spent.
What changes the interval
| Your situation | Interval | Why |
|---|---|---|
| Sediment pre-filter | Every 6-12 months | First line of defense; protects everything after it |
| Carbon pre-filter | Every 6-12 months | Strips chlorine that would shred the membrane |
| RO membrane | Every 2-3 years | The costly heart; lasts if the pre-filters stay fresh |
| Carbon post or polishing filter | Every 12 months | Final taste-and-odor stage before the tap |
| Well water or heavy sediment | Pre-filters every 3-6 months | Grit and iron load them far faster |
| Water tastes off or flow slows | Test TDS, change filters | Both are symptoms of overdue cartridges |
The cost of skipping it
What skipping it costs: a spent carbon pre-filter stops absorbing chlorine, which then reaches the polyamide membrane and degrades it in months instead of years, turning a routine $30-70 annual filter change into a premature $50-90 membrane replacement. Clogged filters also drop the storage-tank pressure until the faucet trickles, and a neglected system can harbor bacteria, which defeats the whole purpose of the setup. Watch the numbers: when a TDS meter shows the output creeping toward your tap water's reading, the membrane is finished. For whole-home coverage, pair it with a whole-house filter.
How to do it (20-30 minutes · DIY, about $30-70 a year in filters)
- Shut the tank ball valve and the feed-water supply, then open the RO faucet to relieve pressure.
- Twist off each filter housing with the supplied wrench and lift out the old cartridges.
- Install fresh cartridges in order (sediment, then carbon pre-filter), and replace the membrane too if it is due.
- Lightly lubricate the housing O-rings, reseat everything hand-tight plus a nudge, and reopen the feed water.
- Flush the new filters for 10-15 minutes, then fill and dump the first full storage tank before you drink from it.
Knowing the interval is the easy half. OnOtto reminds you at the right interval, and it won't let you snooze it into next year. Tasks persist until they're done, and completing RO filter changes schedules the next one automatically.
Put this on autopilot, free for 30 daysFrequently asked questions
How do I know when the RO membrane needs replacing?
Use a handheld TDS meter, which reads total dissolved solids in parts per million. Measure your tap water and your RO output: a healthy membrane rejects roughly 90% or more, so the RO number should be a small fraction of the tap number. When the output TDS climbs and the gap narrows, the membrane is wearing out, typically at the 2-3 year mark. A noticeable drop in how fast the tank refills is another sign. Always change the pre-filters on schedule first, since a fresh membrane behind clogged pre-filters fails early.
Are all RO filters and membranes universal?
Many under-sink systems use standard 10-inch housings, so common sediment and carbon cartridges often interchange, but it is not guaranteed. Membranes in particular vary by capacity (measured in gallons per day) and by housing, so match the model your system calls for. The safest route is to note your system's make and cartridge sizes and buy a matching filter set, which is usually sold as an annual kit. Off-size or mismatched cartridges can bypass water around the filter and defeat the point.
Why is my RO water slow or the tank not filling?
The usual causes are clogged filters, low incoming pressure, or a failing storage-tank bladder. RO needs about 40-60 psi of feed pressure to push water across the membrane, so if the house pressure is low the system crawls. Start by changing overdue filters, then check the tank's air pressure (empty, it should hold a few psi in the bladder). If the whole house runs weak, the issue is upstream, so check your home water pressure before replacing RO parts.
Does RO remove the good minerals, and do I need a remineralizer?
Reverse osmosis strips most dissolved solids, including beneficial minerals like calcium and magnesium, which is why RO water can taste flat to some people. It is not a health problem for a normal diet, but many systems offer a remineralization stage that adds a small amount of minerals back for taste and to slightly raise the pH. It is optional. If you like the taste of your RO water as is, skip it; if it tastes too flat, a remineralizing post-filter is an easy add.