Reverse osmosis (RO) is a popular and highly effective method of water purification used globally. This technology produces water of exceptional purity by removing a vast array of contaminants. However, the effectiveness of RO systems raises questions about the water’s composition and its long-term effects on health. The primary concern is whether stripping water of impurities, specifically natural mineral content, makes it detrimental for regular consumption.
The Purpose and Process of Reverse Osmosis
Reverse osmosis forces water through an extremely fine, semi-permeable membrane at high pressure. This process overcomes natural osmotic pressure, pushing water molecules from a higher concentration of solutes to a lower one. The membrane acts as a molecular sieve, allowing only pure water molecules to pass through while rejecting particles larger than approximately 0.0001 microns.
The process successfully eliminates heavy metals (like lead and arsenic), salts, chemical contaminants (such as fluoride and chlorine), and microorganisms (like bacteria and viruses). RO systems deliver water with a significantly reduced level of impurities, making it a preferred choice where source water quality is questionable. The high purity achieved is the primary purpose of the technology.
The Primary Concern: Demineralization
The core issue with reverse osmosis water stems from the non-selective nature of the purification process. While the semi-permeable membrane rejects harmful contaminants, it also removes naturally occurring, beneficial minerals. Essential electrolytes, such as calcium, magnesium, and potassium, are too large to pass through the membrane.
Mineral content is quantified by measuring Total Dissolved Solids (TDS), typically expressed in parts per million (ppm). RO filtration drastically reduces the TDS to very low levels, often below 50 ppm. This low TDS can make RO water taste “flat” compared to mineral-containing tap water. The result is water that is chemically pure but biologically demineralized.
Removal rates for beneficial minerals are substantial, typically stripping out 92% to 99% of calcium and magnesium. This severe reduction in mineral concentration leads to health concerns. The water is not toxic, but its lack of mineral content changes its physiological interaction with the body.
Health Implications of Drinking Demineralized Water
The primary health concern is the potential for mineral deficiency and disruption of the body’s internal balance. Water low in minerals, or “soft” water, is more aggressive and tends to leach minerals from anything it contacts, including the body’s tissues. This effect can cause the body to excrete more of its own stored electrolytes, such as sodium, potassium, calcium, and magnesium, to maintain osmotic pressure balance. Studies have linked the sustained intake of water low in calcium and magnesium to an increased risk of specific health issues.
Epidemiological research has suggested a possible association between drinking soft water and higher rates of cardiovascular disease mortality. The World Health Organization (WHO) has highlighted these risks, suggesting that drinking water should contain minimum levels of these minerals. Specifically, the WHO recommends a minimum of 20 milligrams per liter (mg/L) of calcium and 10 mg/L of magnesium.
Relying exclusively on demineralized water places a greater burden on the diet to supply all necessary minerals. While water is generally a secondary source of these nutrients, the supplementary intake can be significant for some populations. The risk of deficiency is relevant for individuals whose diets are already low in these minerals. Cooking with demineralized water can also pull minerals out of foods, further reducing the nutrient content of meals.
Strategies for Safe and Healthy RO Water Consumption
Mitigating concerns associated with demineralized water involves reintroducing beneficial minerals after purification. The most convenient solution is a remineralization cartridge or post-filter installed as the final stage of the RO system. These cartridges dissolve small amounts of calcium, magnesium, and sometimes potassium back into the purified water, restoring mineral balance and improving taste.
For those without an inline filter, manual remineralization methods offer flexible alternatives. Liquid trace mineral drops, which are concentrated electrolyte solutions, can be added to individual glasses or pitchers. A small pinch of mineral-rich salts, such as Himalayan pink salt, can also be added, though this requires careful measurement to avoid excessive sodium intake.
It is also prudent to consider the broader dietary context. Since the primary source of calcium and magnesium remains food, a balanced diet rich in vegetables, nuts, and dairy products can compensate for the lack of minerals in RO water. By employing a remineralization technique, consumers can enjoy the superior purity of RO water while maintaining a healthy mineral intake.