Reverse osmosis (RO) water is produced by forcing source water through a semi-permeable membrane at high pressure to achieve a high level of purity. This process effectively removes a wide range of contaminants, including heavy metals, chemicals, and microbes, making the resulting water safe for daily consumption. However, the purification process is non-selective, stripping away naturally occurring dissolved solids, including beneficial minerals like calcium and magnesium. While RO water is generally safe to drink every day, the long-term consumption of this demineralized water presents specific nutritional and health considerations.
The Reverse Osmosis Purification Process
The core of a reverse osmosis system is a tightly wound, semi-permeable membrane that acts as a molecular filter. Water is pushed against this membrane, allowing water molecules to pass through while rejecting almost all larger molecules and dissolved ions. This mechanism effectively removes up to 99% of total dissolved solids, including substances like lead, arsenic, nitrates, and chlorine.
The process separates the incoming water into two streams: the purified water (the permeate) and a concentrated waste stream (the reject or brine) which carries the flushed-out contaminants. This reliance on pressure ensures the resulting permeate is ultra-pure, but it also means beneficial minerals like calcium and magnesium are rejected alongside harmful contaminants.
Health Implications of Demineralized Water
The primary health concern with regular consumption of RO water is the lack of two fundamental minerals, calcium and magnesium. RO systems typically remove 92% to 99% of these minerals from the water source. While drinking water is not the sole source of these nutrients, the minerals present in water are believed to be more readily absorbed by the body than those found in food.
Consuming water low in these elements over a long period can introduce health risks, particularly related to cardiovascular function. Studies suggest that a sustained low intake of magnesium from water may be linked to a higher risk of motor neuronal disease and sudden cardiac death. Similarly, low calcium levels in drinking water have been associated with a higher risk of fractures in children.
The World Health Organization (WHO) recommends a minimum concentration of these minerals in drinking water, such as at least 10 mg/L of magnesium and 30 mg/L of calcium. Water that fails to meet these minimums, like most pure RO water, may not offer the supplementary health benefits of mineralized water.
Demineralized water may also increase the body’s elimination of minerals through diuresis, or increased urination, which can further impact electrolyte balance.
Other Effects of Demineralized Water
The lack of mineral content can cause the water to become slightly acidic and unstable. This allows it to leach trace amounts of metal from plumbing materials and containers it touches. Furthermore, using soft water for cooking can lead to substantial losses of essential elements from food, with losses reaching up to 60% for calcium and magnesium from vegetables.
Strategies for Mineral Replenishment
To mitigate the effects of demineralized water, consumers have several practical options for restoring beneficial mineral content. The most convenient solution is to use a reverse osmosis system that incorporates a dedicated remineralization filter or cartridge. These post-filters automatically reintroduce a balanced blend of minerals, such as calcium and magnesium, back into the purified water just before it leaves the tap.
For those with existing RO systems, manual alternatives are available:
- Liquid trace mineral drops are concentrated solutions that allow for precise control over the mineral dosage.
- An alkaline water pitcher uses mineral media to raise the water’s pH and add minerals like calcium and potassium.
- Adding a small amount of high-quality salt, such as Himalayan pink salt, provides trace minerals. However, meeting significant daily mineral requirements this way would likely exceed recommended sodium intake and alter the taste.
Ultimately, while remineralization methods can enhance water quality, the majority of the body’s required minerals should be sourced from a balanced and varied diet.