Three technologies, three mechanisms. Knowing the difference leads to better specifications.
Overview
Filtration systems can include one or more stages, and each technology works differently. Knowing the mechanism helps when you compare specifications.
PP sediment: physical filtration
Polypropylene depth cartridges trap suspended particles such as sand, silt and rust. They also protect the stages downstream. The micron rating (for example 5 µm) describes particle capture. A PP cartridge is not an adsorbent, and it is not designed to reduce chlorine, taste or dissolved substances.
Activated carbon: adsorption
Activated carbon is highly porous. Substances collect on its internal surface instead of being strained out. The Australian Drinking Water Guidelines (ADWG), the national guideline, describe activated carbon as effective for many taste and odour compounds and for a range of organic contaminants. Performance depends on contact time and flow: in treatment plants, some odour compounds need longer contact than others. The surface's capacity is finite, so media must be replaced on schedule. Carbon form also matters. Granular, powdered and sintered/block carbon behave differently.
Reverse osmosis: membrane separation
RO pushes water through a semi-permeable membrane under pressure. It is the stage used where dissolved salts (TDS) are the issue. RO depends on feed pressure, temperature and membrane condition, and it produces a concentrate stream that needs a drain.
Key buying implications: specs worth checking
- Rated flow and operating pressure
- Media type and form for each stage
- Recommended replacement interval and what it assumes
- Model-specific certification (for example WaterMark for plumbing products)
- Feed-water limits
Be cautious with broad claims
Results depend on the feed water. Ordinary activated carbon should not be presented as a disinfection step. Any claim to reduce a specific substance, PFAS included, needs model-specific test evidence for that substance.
The guideline describes water treatment in general. It does not test or endorse any specific product.
Talk to us
Not sure which combination suits a site? Send us your water test and application.
References
- NHMRC & NRMMC (2011). Australian Drinking Water Guidelines 6 2011, Version 4.0, updated June 2025. Part 2, Chapter 8, section 8.3.3 “Adsorption”. Accessed 7 Nov 2026 (AWST).
- NHMRC & NRMMC (2011). Australian Drinking Water Guidelines 6 2011, Version 4.0, updated June 2025. Part 5, Treatment chemicals: “Carbon, granulated activated” (endorsed 2005). Accessed 7 Nov 2026 (AWST).
- NHMRC & NRMMC (2011). Australian Drinking Water Guidelines 6 2011, Version 4.0, updated June 2025. Part 5, Treatment chemicals: “Carbon, powdered activated” (endorsed 2005). Accessed 7 Nov 2026 (AWST).
- NHMRC & NRMMC (2011). Australian Drinking Water Guidelines 6 2011, Version 4.0, updated June 2025. Part 5, Physical and chemical characteristics: “Taste and Odour” (endorsed 2011). Accessed 7 Nov 2026 (AWST).