Does Reverse Osmosis Remove Minerals? What Australian Homes Need to Know

What Exactly Does Reverse Osmosis Remove?

The RO membrane is a semi-permeable barrier with pore sizes of approximately 0.0001 microns — small enough to block dissolved ions and molecules. In practice, a quality RO system with carbon pre-filtration removes:

The key takeaway: RO is non-selective. The same membrane that removes PFAS and fluoride also removes calcium and magnesium. You can’t configure a standard RO system to remove contaminants while retaining beneficial minerals. They are all dissolved solids and the membrane treats them accordingly.

Does Mineral-Free Water Leach Minerals From Your Body?

This claim circulates widely in online discussions about RO water. The concern: low-mineral water may leach electrolytes from your blood and tissues, creating a net mineral deficit.

The evidence is weak. Your blood mineral concentration is regulated by the kidneys, not the mineral content of drinking water. Kidneys continuously adjust urinary mineral excretion to maintain homeostasis regardless of water TDS. The WHO reviewed this question specifically in their 2004 report on low-mineral water and found no evidence of adverse health effects from consuming demineralised water in populations that ate a normal diet.

The practical context: dietary mineral intake from food is orders of magnitude larger than intake from water. Even if you drink 2 litres of water per day, the calcium contribution from water (say 50mg/L in moderately hard water) represents about 5–10% of recommended daily intake. RO water at 5mg/L calcium reduces this contribution to roughly 0.5% of daily intake — negligible if your diet includes dairy, leafy greens, or nuts.

Exception: People on very restricted diets, those with high fluid intake (athletes), or those with known calcium/magnesium deficiency may have a more meaningful reliance on water minerals. For these groups, remineralisation is worth considering.

Australian Context: Where Mineral Content Actually Matters

In Australia, the mineral content of your water depends heavily on your location:

• Adelaide and Perth: Very hard water from limestone aquifer sources. High calcium and magnesium (TDS 200–500 ppm). RO output here is noticeably flatter-tasting. Remineralisation of RO water is more relevant here because residents are accustomed to hard water taste.
• Brisbane and SEQ: Moderately hard to soft water depending on storage. Wivenhoe/Somerset dam supply is soft (TDS 30–80 ppm). RO output in SEQ is already very close to remineralised water in mineral content.
• Sydney: Soft water from sandstone catchments. Warragamba Dam TDS typically 30–50 ppm. RO output minimally different from source in mineral terms.
• Melbourne: Very soft, acidic water from Silvan/Thomson reservoirs. TDS typically 20–40 ppm. RO water here is borderline acidic (pH 5–6 without remineralisation stage).

For Melbourne and Sydney households, the mineral content argument for remineralisation is minimal — source water already has low mineral content. For Adelaide and Perth households, remineralisation makes a meaningful difference to taste and may matter for households that previously relied on water as a calcium/magnesium source.

Remineralisation Options

Option 1: AquaTru Alkaline Upgrade (Calcium Carbonate Stage)

The AquaTru Classic and Carafe models accept an optional Stage 4 alkaline filter that adds calcium and magnesium back to the RO-filtered water. This is the cleanest solution for existing AquaTru owners: the fifth-stage alkaline filter raises pH to approximately 7.5–8.0 and adds 10–30 mg/L calcium and magnesium — enough to restore a more natural mineral balance and slightly improve taste.

The alkaline stage replaces the standard activated carbon polishing filter. No additional hardware required — it uses the same filter housing.

Option 2: AquaTru Classic with Alkaline Remineralisation Upgrade

The AquaTru Classic is a 4-stage countertop RO (NSF 58 + 401 certified) that removes fluoride (>96%), PFAS (>99%), chloramine, lead, and nitrates. An optional alkaline filter cartridge — the AquaTru Alkaline Filter — slots into the final stage and restores calcium, magnesium, and potassium while raising pH to approximately 8–9. No plumbing required. Available on Amazon AU with Prime delivery.

Option 3: Mineral Drops

Concentrated mineral solutions (typically magnesium chloride or calcium/magnesium trace mineral blends) added to RO water directly. These are inexpensive and allow you to control exact mineral additions. Limitations: requires manual addition every time you refill, and quality varies significantly between brands. Most do not include calcium carbonate specifically (which also raises pH).

Not a product we specifically endorse here, but worth knowing the option exists for existing RO users before purchasing a new system.

Option 4: Don’t Remineralise — and That’s Fine

For most Australians eating a normal diet, mineral-free RO water is not a health concern. The primary reason to get an RO system is to remove PFAS, fluoride, nitrates, heavy metals, and chloramine — and RO does this extremely well. If your diet is adequate in calcium and magnesium, the mineral content of your drinking water is a minor consideration.

Remineralisation is most valuable for taste (RO water at TDS <10 ppm tastes flat to many people) and for households in Adelaide/Perth that are accustomed to and may rely on harder water.

Does an RO System Without Remineralisation Produce Acidic Water?

Yes, typically. Standard RO water with TDS 5–30 ppm often has a pH of 5.5–6.5 — mildly acidic. This is because RO removes the buffering minerals (calcium, magnesium bicarbonates) that keep tap water at neutral pH 7–8. CO₂ from the atmosphere dissolves into the water, forming carbonic acid, which is not removed by the RO membrane.

Whether mildly acidic water (pH 6) is a health concern is contested. Most gastroenterologists consider stomach acid (pH 1.5–3.5) as rendering the slightly acidic pH of drinking water irrelevant to internal body pH. Where acidity does matter: corrosion of copper plumbing and potential effects on tooth enamel with high-volume consumption. A calcium carbonate remineralisation stage raises pH to 7–8 and eliminates both concerns.

What to Look For in an RO System for Australian Conditions

• NSF/ANSI 58 certification for PFAS removal: The AquaTru Classic has this. Many cheaper under-sink systems do not. PFAS contamination is widespread in Australian water supplies (QLD, VIC, ACT PFAS detections are well-documented) and NSF 58 is the only meaningful third-party certification for PFAS removal claims.
• Pre-filtration for chloramine: Australian water supplies use chloramine (not chlorine) as primary disinfectant in most capital cities. Standard carbon block filters are less effective at chloramine removal than catalytic carbon. Look for catalytic carbon or specific chloramine-removal carbon blocks.
• Countertop vs under-sink: See our under-sink vs countertop RO comparison for the full analysis. Short version: countertop RO is easier to install (no plumbing) and produces higher-TDS purified water (typically 10–30 ppm); under-sink produces lower TDS but requires professional installation in most cases.

Recommended RO Systems for Australian Homes

Written by Jayce Love

Former Royal Australian Navy Clearance Diver and TAG-E counter-terrorism operator. Founded Clean and Native to apply the same rigorous thinking to the home environment.

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