Reverse osmosis (RO) is a water purification technology that removes contaminants by forcing water through an extremely fine filter. The system effectively strips away nearly all dissolved solids, including naturally occurring minerals. This process results in water that is exceptionally pure but significantly lacks the mineral content typically found in spring or tap water.
Understanding the Reverse Osmosis Filtration Process
The purification mechanism relies on a semi-permeable membrane that acts as a highly selective barrier. Water is pushed across this membrane under high pressure, overcoming the natural osmotic pressure that would otherwise draw water toward the side with a higher concentration of dissolved solids. This reversed pressure allows only the tiny water molecules to pass through the membrane’s microscopic pores.
The vast majority of contaminants, including salts, heavy metals, and organic compounds, are physically blocked and flushed away in a separate waste stream. Dissolved minerals, such as calcium, magnesium, and potassium, are also rejected because their hydrated ions are substantially larger than the water molecules passing through. This mechanical rejection rate is remarkably high, often reducing the total dissolved solids (TDS) concentration by 95% to 99%.
Consequently, the resulting RO water typically has a TDS level far below 10 milligrams per liter (mg/L), defining it as demineralized water. The process is not designed to distinguish between harmful contaminants and beneficial minerals; it simply separates everything larger than a water molecule. This comprehensive removal is why the water is considered highly pure, yet also mineral-deficient.
Effects of Drinking Demineralized Water
The lack of minerals in RO water impacts both its palatability and its interaction with the environment it contacts. Water with very low TDS, often below 50 mg/L, is frequently described as having a “flat” or “insipid” taste, unlike mineral-rich water. This taste difference is often the first noticeable consequence for individuals switching to an RO system.
From a health perspective, while the majority of essential minerals like calcium and magnesium are obtained through diet, the World Health Organization (WHO) has noted that very low-mineral water is not considered ideal for regular consumption. Low-TDS water can exhibit “aggressive” properties, meaning it may leach materials from plumbing pipes and storage containers, potentially increasing the intake of undesirable metals. Using demineralized water for cooking can lead to a substantial loss of minerals from foods, such as up to 60% for magnesium and calcium.
Research suggests that long-term consumption of water with extremely low mineral content may compromise the body’s water and mineral metabolism. However, for most people with a balanced diet, the trace amounts of minerals normally provided by drinking water are not the body’s primary source. The concern centers on the low level of beneficial calcium and magnesium ions and the water’s corrosive nature.
Methods for Reintroducing Minerals
Several practical methods exist to reintroduce beneficial elements to RO water. The most convenient solution is a post-filtration remineralization cartridge, which is installed as the final stage of the RO system. These cartridges typically contain calcite or other mineral media that slowly dissolve, adding back a balanced amount of calcium and magnesium to the purified water.
These add-on filters not only restore essential minerals but can also slightly raise the water’s pH, mitigating the mildly acidic nature that can result from the RO process. This approach is automated, ensuring consistent mineral levels without requiring any manual effort from the user.
Another manual option involves using concentrated liquid mineral drops, which contain blends of electrolytes and trace minerals. These drops are added directly to a glass or pitcher of RO water, giving the user precise control over the mineral concentration. Simple additions like a pinch of mineral-rich salt, such as Himalayan salt, can also be used as a budget-friendly alternative.