How Reverse Osmosis Works and Why Minerals Are Removed
Reverse osmosis (RO) is a water purification technology that forces water through a semi-permeable membrane at high pressure. This membrane has tiny pores, approximately 0.0001 microns in size, which are small enough to block nearly all contaminants, including bacteria, viruses, chemicals, and dissolved inorganic solids (minerals).
The Science Behind Mineral Removal
The removal of minerals isn't a flaw in the design but a direct consequence of the RO process's effectiveness. Minerals, such as calcium ($Ca^{2+}$), magnesium ($Mg^{2+}$), and sodium ($Na^+$), exist in water as dissolved ionic compounds. These ions are physically larger than individual water molecules and are therefore unable to pass through the microscopic pores of the RO membrane. They are rejected and flushed down the drain, resulting in water with very low total dissolved solids (TDS).
Essential Minerals Lost
Research shows that RO systems remove a wide range of essential minerals during the filtration process. Key minerals lost include:
- Calcium: Critical for bone health, muscle function, and nerve signaling.
- Magnesium: Involved in over 300 biochemical reactions, including energy production and protein synthesis.
- Potassium: Supports fluid balance, nerve impulses, and healthy blood pressure.
- Sodium: Helps maintain fluid balance and nerve function.
- Zinc: A trace mineral that supports the immune system.
Health Implications of Drinking Demineralized Water
While RO water is microbiologically safe, consuming it as your primary hydration source without mineral replenishment can have consequences, as highlighted by multiple studies and the World Health Organization (WHO).
1. Potential Mineral Deficiency
Over time, relying solely on demineralized water can contribute to a deficiency of essential minerals like calcium and magnesium. Although diet is the primary source for these nutrients, the minerals in water are easily absorbed by the body. The WHO has expressed concerns that long-term consumption of demineralized water may increase the risk of heart and bone diseases.
2. Aggressive, Acidic Water
Water with low TDS is naturally aggressive and can become slightly acidic (low pH). This acidic water may leach metals, such as lead and cadmium, from plumbing and storage tanks over time, potentially contaminating the water. For this reason, remineralization is often a standard step in municipal water treatment after desalination.
3. Altered Body Mineral Balance
When the body consumes demineralized water, it may attempt to balance the electrolyte concentration by drawing minerals from its own tissues. This process can lead to a gradual loss of body minerals over time and potentially cause electrolyte imbalances. Early symptoms can include fatigue and muscle cramps, and can be particularly concerning for children, who are more vulnerable to mineral deficiencies.
Comparison: RO Water vs. Mineralized Water
| Feature | RO Water (demineralized) | Remineralized RO Water | Natural Spring Water (variable) |
|---|---|---|---|
| Purity | Extremely high (removes 95-99% of TDS) | Very high (impurities removed before minerals added) | Varies by source, naturally contains minerals |
| Mineral Content | Low to virtually none | Restored with essential minerals (Ca, Mg, K) | High, depending on geological source |
| Taste | Often described as flat or bland | Improved, crisp taste due to minerals | Flavor profile varies with mineral content |
| pH Level | Can be slightly acidic (<7.0) | Adjusted to a neutral or mildly alkaline range (7.0–8.5) | Varies depending on source; usually neutral or slightly alkaline |
| Health Impact | Long-term use without remineralization can lead to mineral loss | Supports essential bodily functions and hydration | Can be beneficial, but mineral levels are less precise |
How to Remineralize RO Water
For those who choose a reverse osmosis system for its superior purification capabilities, adding minerals back is a simple and recommended process.
1. Use a Remineralization Filter
The most convenient and consistent method is to add a post-remineralization filter to your existing RO system. These cartridges, installed after the RO membrane, contain natural mineral media like calcite and corosex, which dissolve slowly into the water as it passes through. They effectively raise the pH and add a balanced amount of essential minerals, making the water healthier and better-tasting.
2. Add Mineral Drops or Supplements
Liquid mineral drops are a customizable and portable option. A few drops added to a glass or pitcher of water can restore trace minerals. However, it requires manually dosing each glass and can be less precise than a filter. Electrolyte powders are another alternative, particularly useful for athletes, but should be used according to dietary needs and recommendations.
3. Blend with Mineral Water or Add Trace Salts
For a natural approach, you can blend RO water with a high-quality mineral water to increase its mineral content and improve the taste. Another method is to add a tiny pinch of a high-quality mineral-rich salt, like Himalayan pink salt, to a glass. However, the WHO cautions against relying on this method for a significant mineral intake, as it would require an exceedingly high amount of salt.
Conclusion
Yes, RO absolutely does destroy minerals during its highly effective purification process. This happens because the microscopic membrane cannot differentiate between harmful contaminants and beneficial dissolved solids. The resulting demineralized water can be slightly acidic and, over the long term, may contribute to mineral deficiencies if not managed properly. Fortunately, modern solutions like remineralization filters provide a simple and effective way to enjoy the superior purity of reverse osmosis water while restoring the essential minerals vital for taste and health. By understanding this trade-off, consumers can make informed choices to ensure their water is both safe and nourishing.
Optional Outbound Link
For a deeper dive into the health considerations of demineralized water, read the full World Health Organization report on the topic.
