Under-sink filters — two completely different technologies
“Under-sink water filter” covers two product types that perform completely different functions. Most Australian buyers don’t discover this distinction until after installation. Understanding it first saves a significant amount of money and disappointment.
| Technology | What it removes | What it cannot remove | Installed cost |
|---|---|---|---|
| Carbon block (under-sink) | Chlorine, chloramine (catalytic), VOCs, microplastics, some heavy metals, taste/odour | Fluoride, PFAS, dissolved minerals, TDS, nitrates | $400–$900 |
| Reverse osmosis (under-sink) | Everything above + fluoride (90–96%), PFAS (90–99%), TDS, dissolved salts, lead, nitrates | Nothing meaningful at standard pore size | $700–$1,500 |
The decision between these two technologies is not about which is "better" — it is about what you actually need to remove from your specific water supply.
WaterMark — the legal requirement for Australian installation
Any plumbed under-sink water filter in Australia must use WaterMark-certified components and be installed by a licensed plumber. This is a legal requirement under the National Construction Code — not a recommendation. A system that is not WaterMark-certified cannot be legally connected to your mains water supply by a licensed plumber.
WaterMark certification confirms the system meets Australian plumbing standards. It does not verify filtration performance. Verify any WaterMark claim at watermark.org.au before engaging a plumber.
Carbon block under-sink — what suits which city
Standard activated carbon is designed for free chlorine removal. Cities using chloramine — Sydney, Brisbane, Adelaide, Canberra, and outer eastern Melbourne — require catalytic carbon specifically. This is the most common under-sink filter mismatch in Australia.
| City | Disinfectant | Carbon type required | Does it remove fluoride? |
|---|---|---|---|
| Perth (northern zones) | Free chlorine (most) | Standard or catalytic | No |
| Perth (southern zones) | Chloramine | Catalytic carbon | No |
| Sydney | Chloramine | Catalytic carbon | No |
| Melbourne (most suburbs) | Free chlorine | Standard carbon sufficient | No |
| Melbourne (outer east) | Chloramine | Catalytic carbon | No |
| Brisbane | Chloramine — 100% | Catalytic carbon | No |
| Adelaide | Free chlorine | Standard carbon sufficient | No |
| Canberra | Chloramine | Catalytic carbon | No |
| Darwin | Free chlorine | Standard carbon sufficient | No |
| Hobart | Free chlorine (very low) | Standard carbon sufficient | No |
Reverse osmosis under-sink — the comprehensive option
An under-sink RO system is the most comprehensive residential filtration available. It removes fluoride (90–96%), PFAS (90–99%), lead, nitrates, dissolved minerals, chloramine, and most dissolved contaminants at the kitchen tap.
Practical considerations:
- Waste water: RO produces 2–4 litres of drain water per litre filtered. This is an environmental consideration in water-restricted cities like Perth.
- Flow rate: Slower than carbon — a tank stores pre-filtered water. Tankless RO systems produce filtered water on demand at higher cost.
- Mineral content: RO removes beneficial minerals. A remineralisation post-filter stage is advisable for daily drinking use.
- Separate tap: Most under-sink RO systems require a separate filter tap rather than using the main kitchen mixer. This requires a third hole in the bench or sink.
- Maintenance: Pre-filters every 6–12 months, RO membrane every 2–5 years depending on usage and water quality.
What to ask before buying any under-sink system
- What is the WaterMark licence number? Verify at watermark.org.au.
- Is the carbon catalytic or standard GAC? Matters for all chloramine cities. Get it in writing.
- Does it remove fluoride? If yes, it must be RO or specialist media. Carbon block does not remove fluoride.
- What is the annual cartridge cost and are aftermarket cartridges compatible? Systems with proprietary cartridges lock you into the supplier’s pricing.
- What NSF certification does it hold? NSF 42 covers taste/chlorine. NSF 53 covers health contaminants. NSF 58 covers RO. Verify at nsf.org.
FilterOut-reviewed suppliers offering under-sink systems
The following suppliers have been independently reviewed by FilterOut and offer under-sink installation. FO scores reflect overall independent assessment — no supplier pays to appear.
See all 29 reviewed suppliers for your state. How we score →
Under-sink vs benchtop — when each makes sense
| Situation | Better option | Why |
|---|---|---|
| Own your home | Under-sink | Permanent install, cleaner result, no bench space used |
| Renting — can make minor changes | Under-sink carbon block | Most landlords approve minor plumbing changes |
| Renting — no changes allowed | Benchtop carbon or countertop RO | No installation required, removable |
| Want fluoride removed | Under-sink RO | Only reliable residential fluoride removal technology |
| Just want taste improvement | Either | Carbon block sufficient; benchtop is cheaper upfront |
| Want water at multiple taps | Whole-home system | Under-sink only treats one tap |
Frequently asked questions
- Do I need a plumber to install an under-sink water filter in Australia?
- Yes, if the system is plumbed into the mains water supply. Any plumbed connection to mains water in Australia must be installed by a licensed plumber using WaterMark-certified components. DIY plumbing of pressurised water connections is illegal in all Australian states and territories. Benchtop or tap-mount systems that do not make permanent plumbing connections do not require a plumber.
- What is the difference between under-sink carbon and under-sink RO?
- Carbon block filters remove chlorine, chloramine (if catalytic carbon), VOCs, taste and odour compounds, and some heavy metals. They cannot remove fluoride, PFAS, dissolved minerals, or nitrates. Reverse osmosis removes everything carbon does plus fluoride (90-96%), PFAS (90-99%), dissolved minerals, lead, and nitrates. RO costs more and produces waste water.
- Does an under-sink water filter remove fluoride?
- Standard carbon block under-sink filters do not remove fluoride. Only reverse osmosis removes fluoride reliably at the residential level, achieving 90-96% reduction. If fluoride removal is your priority, an under-sink RO system is the correct choice.
- How long do under-sink water filter cartridges last?
- Carbon block cartridges typically last 6-12 months depending on usage and water quality. RO pre-filters last 6-12 months; the RO membrane lasts 2-5 years. Annual maintenance cost ranges from $80-$300 for carbon systems and $150-$400 for RO systems, depending on cartridge format and whether aftermarket cartridges are compatible.