Under Sink RO Water Filter | 5 Stage

A 5-stage under-sink reverse osmosis system — the standard mid-range RO build, adding a dedicated granular activated carbon (GAC) stage between the sediment pre-filter and the carbon block for substantially better membrane protection than the entry-level 4-stage build. For most Australian households on chlorinated municipal supplies, this is the right tier.

Why 5 Stages Outperform 4

The critical difference between the 4-stage and this 5-stage build is the addition of Stage 2 — a granular activated carbon (GAC) stage that handles the bulk of the chlorine load before the water reaches the carbon block. Three practical effects:

• The carbon block stage no longer has to do all the chlorine work alone, so it lasts longer between replacements
• Better chlorine reduction per cartridge service interval — less risk of chlorine breakthrough damaging the RO membrane
• The membrane sees cleaner feed water, reaches its rated lifespan more reliably

For a chlorinated supply (every Australian municipal water source), this matters. The cost difference between 4-stage and 5-stage is small relative to the membrane longevity it buys.

Five-Stage Filtration

• Stage 1 — PP spun sediment filter (5 micron): removes sand, dirt, particulate
• Stage 2 — Granular activated carbon (GAC): removes the bulk of chlorine, odour, fine particulates
• Stage 3 — Carbon block (CTO): secondary chlorine and chemical polish; refines water quality before the membrane
• Stage 4 — TFC RO membrane: the purification stage; manufacturer specification reduces up to 99% of TDS, heavy metals, arsenic, mercury, fluoride, and over 1,000 contaminants
• Stage 5 — Post-carbon polish (acid-washed coconut carbon): smooth, refined taste finish on the permeate water before it reaches the tap

All cartridges 10" × 2.5" standard format. 12 L pressure storage tank for on-demand water at the tap.

What's Included

• 5-stage RO filter system (housings + starter cartridges)
• TFC RO membrane
• 12 L pressure storage tank
• Stainless steel filter faucet
• 1/2" threaded inlet block and valve
• 2 m of 1/4" tubing
• Mounting hardware, pressure-reducing valve
• Opening spanners (10" housing + RO membrane)
• Quick-connect hose fittings
• Installation manual

Service Interval

Replace cartridges every 6–12 months; RO membrane every ~24 months. The 5-stage RO replacement cartridge set covers all five cartridges plus a fresh membrane in one SKU.

Bench-Hole Considerations

This system uses a separate stainless steel filter faucet that requires a dedicated hole in the bench or sink. If your benchtop is stone or you don't want a second tap fixture, consider the 5-stage with 3-way tap bundle instead — same filtration, single fixture, no extra drilling.