Suppliers quote a single number. Here's what's inside it — every housing, fitting, cartridge, and labour hour — plus where the margins live and what the next five years will cost you.
What you'll pay in years 2, 3, 4, 5 — once the install is behind you. This is where proprietary vs standard cartridges makes the biggest difference.
The installed price is only the beginning. Over 5 years, ongoing filter costs can match or exceed the original install.
Perth has some of the hardest tap water in Australia — Water Corporation data puts it at 200–300 mg/L calcium carbonate in many suburbs, up to 350 mg/L in parts of the southern corridor. That's the white chalky scale that destroys hot water systems, blocks shower heads, and halves the life of dishwashers. Addressing it properly adds significantly to system cost, and there are three distinct approaches — each with very different implications for ongoing cost and effectiveness.
TAC uses a polymer bead media (Filtersorb SP3 is the most common) to transform dissolved calcium and magnesium into microscopic crystals that pass through your plumbing without adhering to surfaces. Critically — it doesn't remove the minerals, it neutralises their ability to form scale. That means you keep the minerals (good for taste and health) without the scale damage.
The traditional approach — ion exchange resin replaces calcium and magnesium ions with sodium ions, producing genuinely soft water with a characteristically silky feel. Completely eliminates scale. Used in commercial and industrial settings for decades. For homes it's often overkill, and the ongoing sodium/salt cost and water waste add up.
Magnetic clamps or electronic coil devices that claim to alter the electromagnetic properties of scale-forming minerals as water passes through the pipe. Marketed as no-maintenance, zero-cost alternatives to TAC or salt softeners. They are popular with some residential installers because the margins are excellent and installation takes 10 minutes.
Why TAC sits in the expensive tier: Adding a TAC stage to a standard 3-stage system requires a dedicated large-format housing (typically a tall 10" or 20" vessel), specific Filtersorb SP3 or equivalent media, and correct sizing for your household flow rate — undersizing a TAC vessel renders it ineffective. A properly specified and installed TAC stage adds $350–$650 to your system cost upfront, but the ongoing cost is negligible compared to a salt softener. For Perth households on town water with hardness above 150 mg/L, it is generally the most cost-effective long-term scale solution. Ask your supplier about it during the consultation →
Suppliers make money in different places. Understanding this helps you negotiate and compare quotes meaningfully.
The person recommending your system is typically also the one selling it — and filter cartridge replacements carry the highest margin in the industry, at 50–70%. A system with proprietary cartridges you must buy back from them forever is significantly more profitable than one using standard Big Blue cartridges available anywhere. This doesn't make every installer dishonest — but it does mean the system they recommend enthusiastically may be the one that earns them the most over the next decade, not the one that costs you the least. Ask specifically: "Can I buy replacement cartridges from anyone other than you?" The answer tells you everything about where the long-term profit sits.
Margins are estimated from wholesale price lists, retail pricing, and supplier interviews. Individual suppliers vary. The key insight: if you're on proprietary cartridges, the supplier's long-term revenue is in your filter replacements — not the initial install. That's the incentive structure to be aware of.