What a Water Filter Actually Does — An Engineer's Honest Guide
By Sam Mendez — Chartered Process Engineer (CPEng), Engineers Australia
The water filter market is full of impressive-sounding claims. “Removes 99.9% of contaminants.” “99 stages of purification.” “Advanced nano-technology filtration.” If you’ve tried to buy a filter in the last few years, you’ll know the feeling of staring at a wall of products with completely opaque marketing and no clear way to compare them.
I started AQVO because I had the technical background to see through most of it, and it frustrated me. So here’s what I’d tell anyone who asked me, as an engineer: an honest account of how filters work, what they can and can’t remove, and what to actually look for.
The Main Filter Technologies, Explained
Activated Carbon (AC)
Activated carbon is the most widely used filtration medium in consumer water filters, and for good reason — it’s effective, well-understood, and well-priced. Activated carbon is processed to create an enormous internal surface area (a single gram can have a surface area exceeding 1,000 square metres) through which water passes and contaminants adsorb — meaning they stick to the carbon surface.
Activated carbon is highly effective at removing:
- Free chlorine
- Taste and odour compounds
- Many organic chemicals and volatile compounds
- Some trihalomethanes (disinfection by-products)
Standard activated carbon is less effective at removing:
- Chloramines (requires catalytic activated carbon or KDF media)
- Nitrates
- Dissolved heavy metals (requires additional media)
- Fluoride (requires specific media like activated alumina)
- Bacteria and viruses (not a disinfectant)
Catalytic Activated Carbon (CAC)
A modified form of activated carbon that has been processed to enhance its ability to catalyse the decomposition of chloramines. This is the key media type for Melbourne and other cities where chloramination is used. A filter claiming to remove chlorine that doesn’t specify catalytic carbon is likely underperforming for chloramine-treated water.
KDF (Kinetic Degradation Fluxion)
KDF is a high-purity copper-zinc formulation that works through electrochemical oxidation-reduction (redox) to remove chlorine, heavy metals (lead, mercury, copper), and hydrogen sulphide. It’s frequently used in conjunction with activated carbon because the two media complement each other — KDF removes heavy metals that carbon isn’t suited for, and carbon removes organics that KDF won’t address. KDF also inhibits the growth of bacteria and algae within the filter itself, which is a meaningful advantage in a shower filter where the filter can otherwise become a biological growth medium.
Ceramic and Sediment Filtration
Mechanical filtration using ceramic or wound-fibre media removes particulate matter — sediment, rust, particles — by physical straining. It doesn’t affect dissolved compounds but is important for protecting downstream filter stages and removing visible cloudiness or particles. Important for older properties with ageing plumbing, or for rainwater systems.
Calcium Sulphite
A specialised media particularly effective at removing free chlorine even in cold water, and at high flow rates. Calcium sulphite is sometimes used in shower filters because the contact time between water and media in a showerhead is very brief, and this media performs well in that rapid-contact scenario.
Ion Exchange Resin
Ion exchange resins work by swapping ions in the water — most commonly used to remove hardness (calcium and magnesium) by substituting them with sodium or hydrogen ions. This is the basis of traditional whole-house water softeners. In point-of-use tap filters, ion exchange can address specific dissolved minerals and reduce hardness.
What’s Actually in the AQVO Shower Cartridge
You’ll see shower filters advertised with “15 stages” or “17 stages”. Our supplier’s own marketing uses that language too. We don’t, because the number of layers tells you nothing about performance, and I can’t verify every layer independently.
What I can tell you is what the supplier’s data sheet states: the cartridge is about 70% dechlorination media, which does the work of reducing free chlorine, and about 30% mineral media (tourmaline and mineralised ceramic balls), which we describe as a water-feel component only — we make no health or performance claim for it. The supplier’s testing puts free-chlorine reduction at up to 98%. That is supplier data, not NSF/ANSI 177 or an independent Australian laboratory result, and the test conditions aren’t stated. A shower filter is also less effective on chloramine than on free chlorine, and we say so on the product page.
What Filters Don’t Do
I think this section is as important as everything above, and most filter companies skip it entirely.
Filters are not water purifiers. A point-of-use filter — including AQVO’s — is designed to improve water that is already safe. It is not designed to make unsafe water safe. If you have reason to believe your water has serious biological contamination (for example, a boil water alert has been issued), do not rely on a standard carbon filter. Boil the water as instructed by your utility.
Filters require replacement. Every filter medium has a finite capacity. When it’s exhausted, the filter either passes contaminants through or becomes a site of bacterial growth. A filter that’s past its service life can be worse than no filter at all. This is why we state the rated capacity plainly (about 20,000 L for the shower cartridge) and sell replacement cartridges as a one-off purchase — no subscription — so you can replace on your own schedule.
Not all contaminants are the same. A filter that removes chlorine doesn’t remove nitrates. A filter that removes sediment doesn’t remove dissolved lead. Understanding what’s in your specific water, and matching the filter media to that, matters.
Filter ratings should be independently verified. Look for NSF/ANSI certification where available. NSF International is an independent third-party body that tests filter media against specific contaminant reduction claims. A filter claiming to remove a contaminant without independent testing is making an unverified claim.
How to Choose the Right Filter
- Know your water source. Mains water in Melbourne? Chloramine is your primary concern. Mains water in Perth? Chlorine and hardness. Rainwater? Sediment and biological risk.
- Match the media to the target. Chloramine requires catalytic carbon or KDF. Heavy metals require KDF or specific media. Sediment requires mechanical filtration.
- Check for independent testing. Not just marketing claims.
- Factor in maintenance. A cheap filter with expensive cartridges, or a filter with no replacement reminder system, is a filter that will be left in place too long.
- Consider both tap and shower. Most people filter their drinking water and ignore their shower water — but a hot shower is a real exposure route to chlorine too, through steam and skin contact.
Why AQVO Specifies What It Does
The AQVO range is specified around what treated Australian mains water actually contains — chlorine (and chloramine in some networks), plus the taste and odour compounds carbon handles — rather than around a list of things it can’t credibly claim. It isn’t a purifier, and I won’t describe it as one.
The goal was never to sell the cheapest filter or the one with the most impressive-sounding claims. It was to offer one I can stand behind professionally: honest about what it does, clear about what it doesn’t, and sold to people I assume are capable of understanding the difference.
You’ve read this far. I think you are.