If you're researching water filters for your home, you've likely come across two very different technologies: gravity filters and reverse osmosis (RO) systems. Both produce cleaner water than straight tap water. But they work in completely different ways, suit different households, and deliver very different results — including some important differences most people don't know about.
This guide breaks down exactly how each system works, what it removes, what it keeps, and which one makes sense for you.
How They Work
Gravity Filtration
A gravity filter works exactly as the name suggests: water is poured into an upper chamber and pulled downward through a series of filter media by gravity alone. No electricity, no pressure, no plumbing required. The water passes through each filter stage — typically ceramic, activated carbon, mineral media, and sometimes additional stages — before collecting in a lower chamber ready to drink.
Because gravity is the only driving force, the flow is slow and deliberate. That slow pace is actually an advantage: maximum contact time with each filter stage means each medium has time to do its job thoroughly.
Reverse Osmosis
Reverse osmosis uses pressure — either from your mains water supply or an electric pump — to force water through a semi-permeable membrane with pores as small as 0.0001 microns. This membrane is fine enough to block almost everything: bacteria, viruses, dissolved solids, heavy metals, fluoride, nitrates, and more.
Most RO systems are installed under the sink and plumbed directly into your water line. The filtered water is stored in a small pressure tank, with a dedicated tap on the benchtop. RO systems also produce wastewater: for every litre of filtered water produced, anywhere from 2 to 5 litres is flushed to drain.
What Each System Removes
| Contaminant | Gravity Filter (Genzon 5-stage) | Reverse Osmosis |
|---|---|---|
| Chlorine & chloramines | ✓ Activated + catalytic carbon | ✓ Pre-carbon stage |
| Heavy metals (lead, mercury, cadmium) | ✓ Ion exchange resin | ✓ RO membrane |
| Bacteria & cysts | ✓ 0.2-micron ceramic + colloidal silver | ✓ RO membrane |
| Sediment & rust | ✓ Ceramic pre-filter | ✓ Pre-filter |
| PFAS / forever chemicals | ✓ Activated carbon + ion exchange | ✓ RO membrane (partial) |
| Microplastics | ✓ Ceramic stage | ✓ RO membrane |
| Fluoride | Partial reduction | ✓ High reduction via membrane |
| Nitrates | Partial via ion exchange | ✓ High reduction via membrane |
| Dissolved salts / TDS | Not removed | ✓ Significantly reduced |
| Beneficial minerals retained | ✓ Yes — minerals added back | ✗ Stripped out with everything else |
| Natural alkalinity | ✓ pH 7.5–9.0 | ✗ Often acidic (pH 5–6) |
| Ionised water | ✓ Magnetic tap (Genzon) | ✗ |
The Mineral Problem with Reverse Osmosis
This is the issue that changes the conversation for a lot of people once they learn about it.
Reverse osmosis is extraordinarily effective at removing contaminants — because it removes everything. The RO membrane doesn't distinguish between harmful dissolved solids like lead and beneficial ones like calcium and magnesium. Both get stripped out. What comes out the other side is water with very low total dissolved solids (TDS) — sometimes called "dead water" in the industry.
Drinking demineralised water over the long term is a concern that has been raised by the World Health Organization, which noted that water low in minerals may have adverse effects on the body, including increased excretion of minerals and reduced intake of calcium and magnesium from water.
Many modern RO systems attempt to address this by adding a remineralisation stage at the end of the filtration process. This is better than nothing, but the minerals added back are typically basic calcium carbonate — not the complex blend of deep-sea trace minerals that a quality gravity filter provides naturally.
A premium gravity filter like Genzon takes the opposite approach: it starts with filtration and ends with mineralisation, passing water through deep-sea mineral stones sourced from 300–600 metres below the ocean surface. The result is water that's naturally alkaline, rich in calcium, magnesium, and potassium, and tasting noticeably different from the flat, slightly acidic output typical of reverse osmosis.
Practical Differences: Installation, Cost, and Waste
Installation
A gravity filter requires zero installation. Place it on your bench, fill the top chamber, and start drinking better water the same day. No plumber, no drilling, no modifications to your kitchen. This makes gravity filters ideal for renters and apartments, as well as anyone who simply doesn't want the disruption of an under-sink installation.
Reverse osmosis systems typically require professional installation: a hole drilled in your benchtop for the dedicated tap, connections to your mains water line, and fitting of the storage tank under the sink. For renters, this is often not possible without landlord permission. Installation costs typically run $200–$400 on top of the unit price.
Cost
Entry-level RO systems start around $300–$500, with installation on top. Premium systems with remineralisation stages run $800–$2,000+. Annual filter replacements (membrane plus pre and post filters) typically cost $100–$300 per year.
The Genzon 12L gravity filter is currently $346.50 (on sale from $495), with replacement cartridges available at low cost. Running cost is under $0.10 per litre — comparable to RO on a per-litre basis once you factor in the water waste.
Water Waste
This is one of the most significant environmental drawbacks of reverse osmosis. For every litre of filtered water produced, a standard RO system wastes 2–5 litres of water to drain. High-efficiency systems improve this ratio, but waste is inherent to the process.
Gravity filters waste nothing. Every drop of water poured into the top chamber is filtered and available to drink.
Electricity
Most home RO systems require electricity to run a booster pump, or rely on mains pressure (which still draws on municipal infrastructure). Gravity filters use no electricity whatsoever — making them genuinely off-grid capable and useful in power outages, caravans, camping, or rural properties.
When Reverse Osmosis Makes Sense
Reverse osmosis isn't the wrong choice in every situation. It makes sense when:
- Your water source has very high TDS, salinity, or nitrate levels (common in some rural areas or bore water)
- Fluoride reduction is a primary concern and you want very high removal rates
- You own your home, have a large kitchen, and don't mind professional installation
- You're willing to pay for and maintain a remineralisation stage to restore water quality
For most Australian households on town water supply, however, TDS and salinity are not significant concerns — the main issues are chlorine, chloramines, heavy metals, PFAS, and microplastics. A quality 5-stage gravity filter handles all of these effectively.
Which Should You Choose?
If you want the most complete, most convenient, and most cost-effective solution for everyday drinking water — and you want water that's not just clean but genuinely good for you — a gravity filter is the better choice for most Australian households.
Reverse osmosis wins on raw filtration power, particularly for dissolved solids and fluoride. But it loses ground on minerals, convenience, water waste, installation cost, and the quality of what comes out the other end without remineralisation.
Genzon's 5-stage gravity system represents the best of what gravity filtration can do: ceramic filtration to 0.2 microns, multi-media purification including catalytic carbon and ion exchange, deep-sea mineralisation, colloidal silver protection, and a magnetic ionisation tap. You get clean water, naturally alkaline water, water that tastes the way water is supposed to taste — without wasting a drop, without a plumber, and without an electricity bill.
See the Genzon 12L Purifier — currently $346.50 (was $495) →