- →Under-sink filters treat one tap. Whole-home systems treat every outlet. The right choice depends on whether your problem exists only at the drinking tap or throughout the house.
- ✓Melbourne and Sydney: an under-sink carbon filter is sufficient for most households. Soft water, no scale problem, no appliance damage. Whole-home is rarely justified.
- !Perth and Adelaide (northern suburbs): whole-home carbon + TAC is often genuinely worthwhile. High hardness damages appliances. High chlorine affects showers. The problem is house-wide.
- ✗Whole-home carbon does not remove fluoride, PFAS, or heavy metals. If these are your concern, an under-sink RO at the kitchen tap is more effective and significantly cheaper than a whole-home RO system.
- →A common best-of-both approach in Perth: whole-home carbon + TAC for scale and chlorine, plus under-sink RO for drinking water quality. Addresses all concerns without the cost of whole-home RO.
The fundamental difference
The distinction between under-sink (point-of-use) and whole-home (point-of-entry) filtration comes down to one question: how many taps do you need filtered water at?
Under-sink filters treat water at a single point — typically the kitchen cold tap. Everything else in the house (showers, bathrooms, laundry, outdoor taps, hot water system) runs on unfiltered mains water. The filter is small, installed under the sink or on the benchtop, and addresses the water you actually drink and cook with.
Whole-home systems install where the water enters your property — before it branches to any tap in the house. Every outlet receives filtered water: drinking water, shower, bath, laundry, hot water system, outdoor taps. The filter is larger, more complex, typically requires a licensed plumber to install, and costs significantly more.
Neither is inherently better. The right choice depends on why you want filtered water and what's actually in your water.
When an under-sink filter is the right choice
For the majority of Australian households in capital cities with good-quality mains water, an under-sink filter is sufficient. It addresses the main complaint — taste and odour from chlorine or chloramine — at the point where it matters most: drinking and cooking water.
Under-sink filtration is appropriate when:
- Your primary concern is taste and drinking water quality — chlorine, chloramine, sediment
- You want to remove specific contaminants from drinking water: PFAS, lead, fluoride, nitrates (RO under-sink)
- You are in Melbourne, Sydney (inner metro), or Canberra — soft water, no significant hardness, no scale problems
- You are renting or cannot make permanent plumbing changes
- Your budget is limited — under-sink systems cost $200–$800 installed vs $1,500–$4,000+ for whole-home
- You want RO filtration — whole-home RO is impractical and wasteful for most households
When a whole-home filter is worth considering
Whole-home filtration is most justified when the problem extends beyond drinking water — when your water causes problems at multiple points in the house. The clearest cases are:
- Hard water damage to appliances and plumbing: Perth (100–300+ mg/L hardness), Adelaide northern suburbs (120+ mg/L), Brisbane outer suburbs. Scale accumulates in hot water systems, dishwashers, washing machines, shower screens, and tapware. A whole-home TAC or carbon + softener system addresses this at the source before water enters any appliance.
- Bore water for irrigation with iron staining: In Perth, bore water iron stains paths, walls, and fences. A whole-home iron removal system upstream of all outlets prevents staining.
- High chlorine affecting shower/bath experience: Chlorine and chloramine absorb through skin and inhale as steam in hot showers. This is a legitimate reason for whole-home carbon filtration, particularly in Adelaide where chlorine residuals are high.
- Skin and hair sensitivity: Some people notice a genuine improvement in skin and hair condition when showering in filtered water. This is most relevant in high-chlorine or high-hardness areas.
- Tank or bore water as the primary supply: When the whole house runs on untreated private water, whole-home treatment is essential.
City-by-city — what most households actually need
| City | Hardness | Disinfectant | Scale problem? | Recommended starting point |
|---|---|---|---|---|
| Perth | 100–300+ mg/L | Chlorine | Yes (many suburbs) | Whole-home carbon + TAC for hardness |
| Adelaide (north) | 120–133 mg/L | Chloramine | Yes | Whole-home carbon + TAC; high chloramine taste |
| Adelaide (east/hills) | 80–110 mg/L | Chloramine/chlorine | Moderate | Whole-home carbon; consider TAC |
| Brisbane (outer) | 100–120 mg/L | Chloramine | Moderate | Under-sink for drinking; consider whole-home if concerned about scale |
| Brisbane (inner) | 80–100 mg/L | Chloramine | Mild | Under-sink chloramine-rated carbon filter |
| Sydney | 30–58 mg/L | Chloramine | No | Under-sink chloramine-rated carbon filter |
| Melbourne | 15–29 mg/L | Chlorine | No | Under-sink optional; mains water is very good |
| Canberra | ~40 mg/L | Chlorine | No | Under-sink if taste is a concern; no hardness issue |
The cost reality
The 10-year cost difference between under-sink and whole-home filtration is significant and worth understanding before purchase:
| System type | Install cost (approx) | Annual cartridge cost | 10-year total (approx) |
|---|---|---|---|
| Under-sink carbon block (NSF 42/53) | $200–$400 | $80–$150 | $1,000–$1,900 |
| Under-sink RO + remineralisation | $500–$900 | $150–$300 | $2,000–$3,900 |
| Whole-home carbon (single stage) | $600–$1,200 | $150–$300 | $2,100–$4,200 |
| Whole-home carbon + TAC | $1,500–$2,500 | $300–$500 | $4,500–$7,500 |
| Whole-home carbon + salt softener | $1,800–$3,000 | $400–$700 + salt | $5,800–$10,000 |
| Whole-home carbon + TAC + under-sink RO | $2,200–$3,500 | $400–$650 | $6,200–$10,000 |
Many Perth and Adelaide households genuinely benefit from both: a whole-home carbon + TAC system to address scale and chlorine throughout the house, plus an under-sink RO or carbon unit for high-quality drinking water at the kitchen tap. This combination addresses all water quality concerns without the cost and wastefulness of whole-home RO.
What a whole-home carbon filter does NOT do
Whole-home carbon filtration addresses chlorine/chloramine taste, sediment, and some organic compounds. It does not:
- Remove fluoride (only RO does)
- Remove PFAS (only RO or activated carbon at specific contact time)
- Remove dissolved heavy metals in ionic form (e.g., lead, arsenic — need RO or specific media)
- Remove nitrates, dissolved salts, or sodium
- Remove hardness (needs TAC or salt softener as a separate stage)
This distinction is frequently blurred in whole-home sales presentations. If a supplier tells you their whole-home system removes PFAS or fluoride, ask specifically: which stage, to what NSF standard, and what is the cartridge capacity before the claim is no longer valid?
For most Australians outside of Perth and Adelaide's harder suburbs, an under-sink filter is sufficient and significantly more cost-effective. The case for whole-home filtration is strongest when hardness damages appliances, when high chlorine affects showers, or when you have a private water supply. If in doubt, start small — a good under-sink filter at the kitchen tap solves the drinking and cooking water problem for most households.
Use our city water quality guides to understand your specific supply, and our comparison tool to evaluate suppliers based on the system type you actually need.