Under-sink water filters are booming in Aussie homes, but which style suits you best? The two main options are a tankless reverse osmosis water filter and a traditional undersink RO system with a pressurised storage tank. Both deliver reverse osmosis water under the sink, but they work differently and fit different kitchens, budgets, and lifestyles. This guide explains each, compares pros and cons, covers real-world Australian considerations.
Which One Suits You?
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Choose tankless RO if you want compact size, on-demand flow, better water efficiency, and modern features. Ideal for small kitchens or anyone who wants a sleek, smart undersink reverse osmosis system.
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Choose traditional RO (with tank) if you want the lowest upfront price and simple, power-free operation, and you’ve got cupboard space to spare.
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Renters vs owners: Renters often prefer tankless (with a 3-way mixer tap) to avoid drilling; owners can pick either.
How Each System Works
What is a tankless reverse osmosis water filter?
A tankless RO filters on demand. Turn on the RO tap, an internal pump pushes water through pre-filters, the RO membrane, and a post filter in real time. There’s no storage tank, so there’s less stagnation, faster “from-zero” recovery, and a compact footprint. Many models add smart features (TDS display, leak sensors, filter-life alerts).
What is a traditional undersink RO system with a tank?
A traditional undersink RO makes pure water slowly and stores it in a 5–12L pressurised tank. Open the faucet and you get a strong burst from the tank. Drain the tank (filling bottles, cooking), and flow slows to a trickle until it refills. It’s simple, proven, and usually cheaper, but the tank takes up space and water can sit for longer.
Pros & Cons at a Glance
| Tankless RO | Traditional Tank RO | |
|---|---|---|
| Footprint | Compact; frees up 50–75% under-sink space | Bulky tank + housings take cabinet space |
| Flow & recovery | Continuous, on-demand; no “running out” | Fast until tank empties; then slow refill |
| Water freshness | No stored water; less stagnation risk | Stored water can sit; occasional sanitise |
| Efficiency (wastewater) | Often 2:1 to 3:1 (pure:reject) | Older units ~1:3–1:4; (pure:reject) |
| Maintenance | Quick-twist cartridges; clean install | More housings; periodic tank sanitising |
| Leak points | Fewer connections in one module | More lines, fittings, and tank valve |
| Remineralisation | Often built-in on premium units | Sometimes add-on stage |
| Noise | Low hum from internal pump | Silent (uses mains pressure) |
| Price range | Higher upfront | Lower upfront |
| Install difficulty | Needs power outlet; 3-way tap friendly | No power needed; often needs a faucet hole |
| Cabinet fitment | Great for tight spaces, bins/drawers | Can clash with bins/corner sinks |
| Lifespan | Long with proper service | Long with proper service |
Real-World Considerations for Aussie Kitchens
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Small cabinetry & corner sinks: Tankless wins on space; easier to keep bins, pull-outs, and cleaning gear under the sink.
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Plumber access & compliance: Pick WaterMark-certified gear for mains connection and insurance peace of mind.
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Mains pressure variability: Tankless models use a pump for consistent flow; tank systems depend on your line pressure.
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Rentals (non-destructive): Tankless + 3-way mixer tap avoids drilling a new RO faucet hole—easy to remove when moving.
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Chlorine/chloramine & taste: Either undersink RO option removes chlorine by taste and odour via carbon + membrane.
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Fluoride concerns: Only a few methods reliably remove fluoride; Reverse osmosis is the most practical water purifier that removes fluoride at home.
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Local issues (PFAS, hardness pockets): RO handles PFAS, heavy metals, nitrates. Add UV on some traditional rigs for rainwater/bore supplies if needed.
Aquala P500 vs. Typical Options
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On-demand filtration (no tank): Fresher taste and no stagnation risk versus stored-water systems.
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Cabinet space saved: Tankless chassis replaces the tank + housings, freeing room in tight Aussie kitchens.
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Simple cartridge changes: Front-load, quick-twist filters with smart alerts = 60-second maintenance.
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Flow & noise: Powered pump delivers steady flow for everyday use; a soft hum replaces the need for high mains pressure.
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Wastewater ratio: Modern tankless designs target ~1:1–1:2 pure-to-waste (vs traditional’s 1:3–1:4), saving thousands of litres yearly.
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Remineralisation option: Alkaline stage returns calcium/magnesium for crisp taste so RO water doesn’t taste “flat.”
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WaterMark/compliance: Built for Australian plumbing standards; check your unit’s certification before install.
Buyer’s Checklist (60-sec Decision Guide)
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Cabinet space: Tight? Go tankless. Spacious? Either works.
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Daily litres: Big family / high use? Tankless = never “running out.”
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Taste priorities: Prefer mineral feel? Choose a unit with remineralisation.
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Maintenance comfort: Want tool-free, clean swaps? Tankless. Don’t mind canisters and tank sanitising? Traditional’s fine.
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Rental vs ownership: Renting and can’t drill? Tankless + 3-way tap.
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Local water issues: Need water filter that gets rid of fluoride or PFAS? Either RO works; confirm spec sheets.
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Budget now vs later: Traditional is cheaper upfront; tankless often wins on water efficiency, space, and experience.
FAQ
Does a tankless RO waste less water than a traditional undersink RO system?
Typically yes. Tankless designs commonly reach ~2:1–3:1 pure-to-waste. Many traditional systems sit around 1:3–1:4 unless upgraded (e.g., permeate pump).
Is reverse osmosis water under sink installation DIY-friendly in Australia?
Often, yes, if the unit is WaterMark-certified and you’re comfortable with basic plumbing. Otherwise, a licensed plumber can fit it quickly, especially where regulations require it.
Do I need remineralisation with undersink reverse osmosis?
Pure RO can taste flat. A remineralisation stage adds calcium/magnesium for balanced taste and mouthfeel, common on premium ro filter units.
How often do cartridges need changing on a tankless ro?
Pre-filters ~6–12 months; RO membrane ~2 years; remineralisation ~12 months (usage and water quality dependent).
Will an undersink ro reduce water pressure at the mixer?
No. RO water usually dispenses via a dedicated faucet or a 3-way tap channel, so your main mixer pressure stays the same. Tankless pumps help maintain steady RO flow.
Conclusion
Bottom line: If you want compact design, on-demand purity, modern monitoring, and better efficiency, a tankless reverse osmosis water filter is a joy to live with. If you’d rather minimise upfront spend and don’t mind a bulky tank, a traditional undersink RO remains a proven workhorse. Either way, you’ll enjoy great-tasting water, minus chlorine, PFAS, heavy metals, and—if you choose—fluoride, thanks to a water purifier that removes fluoride at the point of use.
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View Aquala P500: See how a modern tankless ro water filter fits Aussie kitchens (compact, efficient, remineralised).
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Get a personalised recommendation: Tell us your space, water, and budget, we’ll match you with the right water filtration system that removes fluoride and the rest.
