Pre-filtration
PP, CTO, and UDF cartridges remove sediment, chlorine, and organics to protect the membrane.
RO Technology
Stages of RO Systems
Reverse osmosis is one stage in a multi-filter system — learn how prefilters, the membrane, and post-filters work together.
More than just a membrane
Reverse osmosis is only one stage in an RO system. AquTai systems are built with 5 or 7 stages depending on source water chemistry and the contaminants present. Water is always treated with reverse osmosis in conjunction with prefilters and post-filters — each playing a specific role in delivering safe, great-tasting water.
Water Flow
Three phases of treatment
Feed water passes through each phase in sequence before reaching your tap.
RO membrane
Pressurised separation rejects dissolved solids, bacteria, and viruses at sub-micron level.
Post-treatment
Carbon polishing, remineralisation, and alkaline filters balance taste and pH after storage.
System Configurations
5-stage vs 7-stage systems
The right configuration depends on your water quality goals and local source water conditions.
Essential purification
Includes pre-filtration (PP, CTO, UDF), the RO membrane, and a post-carbon filter. Ideal when you need reliable contaminant removal and improved taste without additional mineralisation.
- Stages 1–3: pre-filtration
- Stage 4: RO membrane
- Stage 5: post-carbon polish
Full treatment & balance
Adds mineralised and alkaline post-filters to restore minerals and raise pH. Suited for drinking water where taste, mineral content, and alkalinity matter.
- Stages 1–5: as 5-stage system
- Stage 6: mineralised filter
- Stage 7: alkaline filter
Filter Types
What each stage does
Every filter in an AquTai RO system is selected for a specific job — from trapping visible rust particles to restoring minerals in the final drinking water. Replacing cartridges on schedule keeps performance consistent and protects the membrane.
- Prefilters are replaced more frequently — they protect downstream stages
- The RO membrane typically lasts 2–3 years with proper pre-treatment
- Post-filters polish water after it leaves the storage tank
All Seven Stages
Filter-by-filter breakdown
Each type of system contains one or more of the following filters.
Stages 1–3
Pre-filtration
Protects the RO membrane by removing sediment, chlorine, and organic contaminants before pressurised separation.
1
Pre-filtration
PP Filter
A polypropylene sediment cartridge removes visible particles — sand, silt, dirt, rust, and other suspended solids. A 0.5 micron PP filter traps particles larger than 0.5 microns, protecting downstream filters and the RO membrane. Economically priced and easy to replace when it clogs.
2
Pre-filtration
CTO Filter
An extruded carbon block (CTO) cartridge made from coconut-shell carbon adsorbs chlorine, VOCs, and chemicals that affect taste and odour. Its dense structure is ideal for residential systems where improving water flavour is a primary goal.
3
Pre-filtration
UDF Filter
Granular activated carbon (UDF) is oxygen-treated and broken into granules to maximise surface area. Water passes through, allowing organic matter and residual chlorine to bond with carbon molecules and be removed before reaching the membrane.
Stage 4
RO membrane
The core purification stage where dissolved solids, bacteria, and viruses are rejected under pressure.
4
Core separation
RO Membrane
The heart of every RO system. With pores smaller than 0.0001 micron, the NSF-certified membrane rejects viruses, bacteria, and up to 99% of dissolved solids — including arsenic, chromium, and lead. The same technology used in bottled mineral water production.
Stages 5–7
Post-treatment
Polishes, remineralises, and balances water after storage — optional stages depending on system configuration.
5
Post-treatment
Post Carbon Filter
A high-quality activated carbon filter polishes the stored permeate before it reaches your tap. It removes any residual taste or odour picked up in the storage tank and improves the final flavour of the water.
6
Post-treatment
Mineralized Filter
A remineralisation cartridge restores essential minerals — sodium, potassium, magnesium, and others found in natural mineral water. Long-term use supports balanced drinking water with minerals important for health and body function.
7
Post-treatment
Alkaline Filter
The alkaline filter raises the pH of acidic RO water, adding back ionised calcium, magnesium, sodium, and potassium. The result is alkaline ionised water with a more balanced mineral profile for drinking.
Continue Learning
More about reverse osmosis
Explore the full AquTai RO guide — from theory to applications.
What is Osmosis?
The natural process behind reverse osmosis and how membranes separate pure water.
Read article →How RO Systems Work
From prefiltration and membrane separation to storage tanks and post-treatment.
Read article →Benefits of Safe Water
Why clean drinking water matters for health, hydration, and everyday wellbeing.
Read article →RO Applications
Where reverse osmosis fits — homes, restaurants, laboratories, and industry.
Read article →Find the right AquTai RO system
Browse our domestic, commercial, and industrial reverse osmosis range — configured with the filter stages your application needs.