Reverse osmosis (RO) is a highly effective water purification method that produces water with extremely low levels of dissolved solids. This process removes nearly all contaminants, resulting in a product often described as pure H2O. However, this intense level of filtration raises a fundamental question for consumers: does this purity translate into a healthier drinking water option, or does the removal of all dissolved substances, both harmful and beneficial, ultimately pose a detriment to human health? The answer involves a careful examination of the filtration mechanism, the subsequent lack of minerals, and the water’s chemical characteristics.
The Purification Mechanism
The reverse osmosis process operates by utilizing pressure to force source water through a synthetic, semi-permeable membrane. This membrane is designed with extremely fine pores, typically around 0.0001 microns, that allow water molecules to pass through while rejecting larger molecules and ions. The pressure applied must be sufficient to overcome the natural osmotic pressure that would otherwise draw water into the concentrated side.
This mechanism is highly effective at separating water from a vast array of impurities. The system significantly reduces the concentration of heavy metals like lead and arsenic, chemical residues such as pesticides, and dissolved salts. By stripping the water of these known harmful substances, the RO system achieves a high degree of microbiological safety and chemical purity. The unwanted contaminants are flushed away in a separate, concentrated waste stream, leaving behind the highly purified water.
Concerns Regarding Mineral Depletion
The primary controversy surrounding RO water consumption centers on the removal of naturally occurring beneficial elements, specifically calcium and magnesium. Reverse osmosis filtration can remove between 92 to 99 percent of these dissolved solids, resulting in water that is virtually demineralized. While diet is the main source of these nutrients, water can contribute a measurable percentage of daily intake, especially for populations with lower dietary consumption.
The World Health Organization (WHO) has specifically addressed the consumption of demineralized water, cautioning that it may have a negative influence on the human organism. Water low in dissolved solids can negatively affect the body’s homeostatic mechanisms, compromising mineral and water metabolism. One proposed mechanism suggests that water with low mineral content may lead to an increased elimination of minerals already present in the body through urine.
Long-term consumption of water that lacks these minerals has been linked to potential physiological implications. Observations in some European populations, such as those in the Czech Republic and Slovakia, who adopted demineralized water for drinking, reported health issues suggestive of acute magnesium and calcium deficiency. These complaints included symptoms like muscle cramps, fatigue, and cardiovascular disorders. While RO water is clean, its lack of essential minerals is the basis for most health concerns.
The Role of pH and Water Acidity
Another distinct characteristic of RO water is its tendency toward a slightly acidic pH, separate from the mineral content debate. Purified water from an RO system often measures a pH of 5.0 to 7.0, typically settling around 6.5, which is slightly lower than neutral. This shift toward acidity occurs because the removal of calcium and magnesium also removes the natural buffering capacity of the water.
In the absence of these alkaline mineral buffers, the water is more susceptible to absorbing carbon dioxide from the air, which then forms a small amount of carbonic acid. This process naturally lowers the water’s pH level. However, this slight acidity is not generally considered a health threat to the consumer.
The human body possesses robust homeostatic mechanisms, such as the kidney and respiratory systems, that tightly regulate the blood’s pH balance. The slight acidity of RO water is minimal compared to the acidity of common beverages like coffee or fruit juices. Consequently, drinking slightly acidic RO water does not meaningfully impact the body’s internal pH balance.
Methods for Restoring Water Quality
For individuals who choose to utilize reverse osmosis filtration for its superior contaminant removal but wish to mitigate the issues of mineral depletion and acidity, several post-filtration solutions are available. The most convenient and consistent method is the installation of an inline remineralization cartridge as the final stage of the RO system. These cartridges are specifically designed to reintroduce beneficial minerals back into the purified water before consumption.
These post-filters often contain natural mineral media, such as calcite, dolomite, or a blend of calcium and magnesium compounds. The water passes over these media, dissolving a controlled amount of minerals and increasing the total dissolved solids (TDS) to a more balanced level. This process effectively raises the pH of the water, restoring its buffering capacity and moving it closer to a neutral or slightly alkaline state.
Alternative methods include using alkaline filters or adding concentrated liquid mineral drops directly to the purified water pitcher or glass. Alkaline filters typically use mineral balls or ceramic media to achieve the same result as a cartridge. By reintroducing a balanced profile of minerals, these methods transform the highly pure, but demineralized, RO water into a product that is both clean and nutritionally balanced.