The Science Behind Water Filter Cartridges: How They Work

Water filter cartridges are the working part of any filtration system — but how they actually clean your water depends entirely on what's inside. Here's a plain-English breakdown of the main filtration processes used in Australian home water filters.

See our Benchtop Water Filters Guide, our Reverse Osmosis Guide, or browse our replacement cartridge range.

1. Mechanical Filtration

The simplest process — water passes through a physical barrier with pores measured in microns. Anything larger than the pore size gets blocked. A ceramic dome at 0.9 microns blocks bacteria, Giardia, and Cryptosporidium. A sediment cartridge at 5 microns catches rust, dirt, and sand. The finer the micron rating, the more thorough the filtration — but the slower the flow rate.

2. Adsorption (Activated Carbon)

Activated carbon works like a sponge for chemicals. It has an enormous surface area — one gram of activated carbon can have a surface area of over 500 square metres — which attracts and traps chlorine, chloramines, VOCs, pesticides, and organic compounds as water passes through. This is why carbon filters are so effective at improving taste and removing the chlorine smell common in Australian town water.

Carbon block cartridges (available in 0.5, 1, and 5 micron ratings) are the most common type used in under-sink and benchtop systems. Browse our under-sink cartridge range.

3. KDF Redox Media

KDF (Kinetic Degradation Fluxion) is a copper–zinc alloy that uses a redox (oxidation–reduction) process to reduce chlorine, heavy metals (lead, mercury, copper), and hydrogen sulphide. It also has bacteriostatic properties — it inhibits bacterial growth inside the cartridge. KDF is one of the key stages in our 8-stage KDF cartridge, working alongside ceramic and carbon stages.

4. Mineral and Alkaline Stages

Some multi-stage cartridges include mineral media — Maifan stones, Prill Beads, and bio ceramic balls — that add trace minerals (calcium, magnesium, zinc) and raise the water's pH to approximately 7.5–8.5. This is how our 8-stage KDF system produces mildly alkaline, mineralised water without electricity or ionisation.

5. Reverse Osmosis Membrane

The most thorough filtration available. An RO membrane has pores of just 0.0001 microns — small enough to block dissolved solids, fluoride, heavy metals, nitrates, bacteria, and viruses. Water is pushed through the membrane under pressure, leaving contaminants behind. See our complete Reverse Osmosis Guide for more detail.

Why Cartridge Replacement Matters

A cartridge past its service life doesn't just stop filtering — it can harbour bacteria and release trapped contaminants back into your water. Replace on schedule: most cartridges every 6–12 months, RO membranes every 2–3 years. See our Replacement Filter Cartridges Guide for system-specific intervals.

Frequently Asked Questions