The Basic Principle
Osmosis is a natural process where water moves through a semi-permeable membrane from a lower-concentration solution to a higher-concentration solution. Reverse osmosis does the opposite — by applying pressure to the high-concentration side (your contaminated water), we force water molecules through the membrane against their natural direction, leaving dissolved contaminants behind.
The membrane is the heart of this process. It contains billions of microscopic pores — approximately 0.0001 microns in diameter. For scale, a human hair is about 70 microns wide. These ultra-fine pores allow water molecules to pass, while blocking dissolved salts, heavy metals, organic compounds, and most biological contaminants.
The 5-Stage RO Process
A typical domestic RO system works in stages:
- **Stage 1 — Sediment Filter:** Removes suspended particles — sand, silt, rust, and visible impurities down to 5 microns
- **Stage 2 — Activated Carbon:** Removes chlorine, chloramines, and organic compounds that would chemically degrade the RO membrane
- **Stage 3 — RO Membrane:** The core purification stage. Rejects dissolved salts, heavy metals, fluorides, nitrates, and more at up to 98% efficiency
- **Stage 4 — Post-Carbon:** Final polishing to improve taste and remove any residual odour
- **Stage 5 — UV (in some systems):** Disinfects any remaining biological contaminants
What Does RO Remove?
RO membranes are highly effective at removing:
| Contaminant | Typical Rejection |
|-------------|------------------|
| Dissolved salts (TDS) | 95–98% |
| Heavy metals (lead, arsenic, mercury) | 95–99% |
| Fluoride | 90–96% |
| Nitrates/Nitrites | 85–94% |
| Bacteria & viruses | 99%+ (with UV stage) |
| Chlorine | Removed by pre-carbon (not the membrane) |
Why the Membrane Matters Most
The membrane is the only component in an RO system that actually removes dissolved solids. Pre-filters protect the membrane; post-filters polish the output. But the membrane *is* the purification.
A low-quality or expired membrane dramatically reduces rejection efficiency — you may still get water that looks clean, but TDS rejection can drop from 98% to 70% or worse. This is why membrane quality and regular replacement are the most important factors in RO system performance.
The TFC Membrane Advantage
Modern residential RO systems use Thin Film Composite (TFC) Polyamide membranes — the industry benchmark for performance. TFC membranes offer:
- Higher salt rejection (95–98%+) than older cellulose acetate membranes
- Wider operating temperature range
- Better resistance to bacterial degradation
- Longer effective service life with proper pre-filtration
CLARYN membranes use TFC Polyamide construction.