REVERSE OSMOSIS • FILTERS & MEMBRANES
What each stage in an under-sink RO system does, how the stages differ, and why two systems may use different cartridges. Use this guide to understand what is under your sink, then follow the right service path if you need help.
Not sure which filter you need? Water Fixers can inspect the system, identify the cartridge or membrane, check the housing and O-rings, and replace the correct components.
Reverse osmosis systems use multiple stages rather than one filter doing everything. Sediment filtration helps protect later stages from particles. Carbon filters help with chlorine, taste and odor. Dual-purpose and inline filters combine or polish treatment. The RO membrane is the primary dissolved-solids separation stage. The exact combination depends on the system.
CORE RO FILTERS
These are the most familiar RO service cartridges. Keeping them current helps protect the membrane and maintain taste and flow.
PRE-FILTER
Fine particle pre-filtration
CARBON STAGE
Taste, odor & chlorine stage
POST-FILTER
Final polishing filter
SPECIALTY & INLINE
Some systems add combination, inline, or finishing stages. Water Fixers can match the correct replacement to the system already under your sink.
COMBINATION STAGE
Combined sediment + carbon treatment
OPTIONAL STAGE
Optional finishing stage
INLINE FILTER
Compact carbon polishing
THE RO SEPARATION STAGE
The membrane is different from routine pre-filters and post-filters. If new filters do not restore performance, the membrane, pressure, tank, flow restrictor or another system component may need to be checked.
MEMBRANE
The membrane is the primary separation stage. Feed pressure moves water across a thin-film-composite membrane; treated water goes toward storage while concentrate goes to the drain. Membranes come in different sizes and configurations, so a replacement must match the system. Membrane replacement should be based on verified system performance and operating conditions, not age alone.
HIGH-EFFICIENCY OPTION
A 1-to-1 membrane is used on compatible RO systems designed around that membrane configuration. Because membrane size, flow and plumbing arrangement matter, Water Fixers can confirm the correct replacement before installation.
Use this as a quick orientation—not as a substitute for matching the cartridge to the exact RO system.
Particles, silt and pre-filtration
Often the first protection stage
Chlorine, taste and odor support
Protects water quality and may protect the membrane
Combined particle + carbon treatment
Useful where a system is designed for combination media
Dissolved-solids separation
Checked when filters alone do not restore RO performance
IMPORTANT DURING FILTER CHANGES
Filter replacement can reveal brittle housings, damaged threads, shifted O-rings or cracks that were not obvious before service. If a housing does not line up or seal normally, do not keep tightening it. Shut off the RO water supply and have the system checked.
1
Confirm the system, filter stages and compatible cartridges.
2
Install the correct filters or membrane without forcing worn components.
3
Check housings, O-rings, tubing, fittings, pressure and leak points.
4
Restore water, check for leaks and verify system operation.
If the guide points to a service need, Water Fixers can identify the installed configuration and route the job correctly: routine cartridges to filter replacement, membrane concerns to membrane evaluation, whole-system upkeep to maintenance, and leaks or failures to service and repair.
What are the main stages in an RO system?
Sediment and carbon prefilters, the membrane, a storage tank, and on many systems a polishing carbon stage after the tank. Some systems add a specialty stage.
Do all RO systems use the same filters?
No. Stage count, stage order, housing size and cartridge format differ by system. Confirm the installed sequence before cartridges are ordered.
Is more stages always better?
No. Stage count describes the arrangement, not performance. What matters is whether the supplied cartridge sequence fits the system and water conditions and is maintained correctly.
Where do I get replacement or service help?
Use RO filter replacement for routine cartridges, membrane replacement for membrane-specific evaluation, maintenance for the overall service plan, and service & repair for leaks, low flow, tank problems or other failures.
Water Fixers supports reverse osmosis owners across Santa Maria and the Central Coast. Use this page to understand the stages, then follow the dedicated filter, membrane, maintenance or repair page that matches the job.
Water Fixers Plumbing & Filtration
2893 Industrial Pkwy, Santa Maria, CA 93455
805-928-6444 · License #719792