Reverse osmosis (RO) is a widely adopted method for purifying water. A common question is whether this advanced filtration process removes all minerals. Understanding RO systems’ capabilities and their implications for water composition is important for those seeking cleaner drinking water.
How Reverse Osmosis Works
Reverse osmosis operates on a fundamental principle involving pressure and a specialized semi-permeable membrane. This membrane is designed with microscopic pores, allowing water molecules to pass through while blocking larger dissolved solids and impurities.
The applied pressure overcomes natural osmotic pressure, pushing water from a higher concentration of solutes to a lower concentration. Contaminants, including dissolved salts and minerals, are retained on one side of the membrane and then flushed away in a waste stream. This mechanism ensures the purified water, known as permeate, is significantly cleaner than the incoming feed water.
Minerals: What RO Removes and What Remains
Reverse osmosis is highly effective at removing a wide range of dissolved inorganic contaminants, including most minerals. RO systems typically achieve a 90% to 99.9% removal rate for total dissolved solids (TDS). This includes common minerals such as calcium, magnesium, sodium, and potassium, which are largely rejected by the semi-permeable membrane because their molecules are larger than water molecules.
For instance, RO systems eliminate 94-98% of calcium and magnesium. While RO removes a substantial percentage of these substances, trace amounts of some minerals can still pass through the membrane. The exact effectiveness depends on the specific RO system’s configuration and membrane quality.
Drinking Demineralized Water: Health Considerations
The consumption of water with significantly reduced mineral content, often called demineralized water, raises questions regarding its health implications. While water contributes to daily mineral intake, the primary source of essential minerals for human health is a balanced diet rich in fruits, vegetables, and whole grains. For most healthy individuals with adequate dietary mineral intake, drinking RO water is generally not considered a health concern.
However, some studies suggest that prolonged consumption of water extremely low in minerals, particularly without sufficient mineral intake from food, could potentially lead to issues such as electrolyte imbalance. The World Health Organization (WHO) has noted that demineralized water, if not remineralized, is not ideal for long-term consumption and has suggested minimum levels for certain minerals like calcium and magnesium. These concerns primarily relate to the water’s potential to leach minerals from the body or from food cooked in it, though the overall impact largely depends on an individual’s diet.
The Purpose of Remineralization
Given that reverse osmosis removes a high percentage of minerals, some RO system users choose to remineralize their water. A primary reason for remineralization is to improve the water’s taste. Highly purified water, devoid of minerals, can often taste “flat” or “dead” to many palates. Reintroducing a balanced blend of minerals like calcium, magnesium, and sodium can enhance the flavor, making the water more palatable.
Beyond taste, remineralization also reintroduces beneficial minerals removed during purification. Methods for remineralization vary, including post-filtration remineralization cartridges, which add a controlled amount of minerals back into the water. Other approaches include adding mineral drops or specific mineral-rich salts like Himalayan pink salt to the purified water. These methods aim to restore some natural mineral content, which can also help balance the water’s pH.