What each stage does
| Stage | Job | What wears it out |
|---|---|---|
| Sediment pre-filter | Catches particles | Sediment load; clogs and slows flow |
| Carbon pre-filter | Reduces chlorine or chloramine that can damage membranes | Volume treated and disinfectant level |
| RO membrane | Reduces dissolved solids and certified contaminants | Hardness, chlorine exposure, age |
| Post-filter / remineralizer | Polishes taste; alkaline systems add minerals back | Time and volume |
The EPA's WaterSense specification for point-of-use RO requires certified systems' membranes to last at least a year before replacement, which gives a sense of the scale; your manual governs.
Why your schedule may differ from the box
- Disinfectant: chloramine is harder on carbon than free chlorine, so carbon stages can be the limiting factor in chloramine areas. See chloramine guide.
- Hardness: hard water can scale a membrane faster.
- Sediment: after plumbing work or on well water, pre-filters load up sooner.
- Usage: a large household uses more water through the same cartridges.
- Upstream treatment: a whole-home filter or softener can extend RO stage life.
Signs a stage is due
- The RO faucet runs slower or the tank refills more slowly.
- A chlorine taste or odor returns.
- TDS at the RO faucet climbs compared with readings when the system was new.
- The system runs to drain more than usual.
- It has simply passed the date in the manual.
Using a TDS meter
A handheld TDS meter is a cheap, simple check. Measure tap water and RO water on the same day, and write both down. The percentage reduction should stay fairly steady. A steady rise at the RO faucet usually points to the membrane or a seal. TDS does not measure every contaminant, so it is a health check on the system, not a full water test.
Keep certification valid
If you chose a system for a certified reduction claim, use the replacement cartridges listed for that model. A non-listed cartridge may fit but not perform as certified. Write the install date on each cartridge. For ownership costs, see RO filter replacement cost and RO maintenance and operating costs. Living Water's alkaline RO owners can ask Jorge for the schedule that fits their water.
A simple maintenance routine
- Write the install date on each housing or keep a note inside the sink cabinet.
- Take a TDS reading of tap and RO water every month or two.
- Set a reminder for the pre-filter date in the manual.
- Sanitize the system and tank when the manual calls for it, usually during a filter change.
- Check under the sink for drips at fittings and the drain saddle.
Ten minutes every few months keeps the system working as designed.
https://www.epa.gov/watersense/point-use-reverse-osmosis-systems
https://info.nsf.org/Certified/DWTU/
https://www.cdc.gov/drinking-water/prevention/about-choosing-home-water-filters.html
https://www.epa.gov/dwreginfo/chloramines-drinking-water
Updated 2026-10-17 · Living Waters · Jorge Canela, Water Quality Specialist