Reverse osmosis (RO) is a highly effective water purification method that uses pressure to force water through a specialized semi-permeable membrane. This process separates water molecules from dissolved solids and other impurities present in the source water. The primary purpose of this technology is to reduce the concentration of dissolved contaminants, including various salts, minerals, and chemical species. RO systems are widely used in large-scale desalination plants and smaller home filtration units.
How Effective is Reverse Osmosis at Removing Sodium?
Reverse osmosis is extremely efficient at removing sodium from water, with high-quality systems routinely achieving rejection rates between 95% and 99% of dissolved salts. This rejection rate is the standard metric used to gauge a membrane’s performance. Sodium is a monovalent ion, meaning it carries a single positive charge. In a well-maintained system, the resulting purified water has a significantly lower sodium concentration than the source water.
While sodium is a monovalent ion, generally less rejected than divalent ions like calcium or magnesium, its removal rate remains very high. The exceptional performance of RO membranes makes this technology a reliable choice for individuals requiring a substantial reduction in the sodium content of their drinking water.
The Science Behind Ion Rejection
The mechanism of ion rejection in reverse osmosis is based on applying pressure to overcome the natural process of osmosis. Osmosis is the movement of water across a semi-permeable membrane from low to high solute concentration. In an RO system, a pump applies pressure to the contaminated side of the membrane, forcing the water flow to reverse direction.
This applied pressure overcomes the osmotic pressure, pushing pure water molecules through the membrane’s incredibly fine pores. The pore size is approximately 0.0001 micron, which is small enough to physically block the passage of hydrated sodium ions. Since the sodium ion is electrically charged, it is also effectively repelled by the membrane material, ensuring a high degree of separation from the water stream.
Implications of Removing Sodium and Other Dissolved Solids
The water produced by reverse osmosis has a very low concentration of total dissolved solids (TDS), including sodium, often leading to it being described as “pure” or demineralized water. This high degree of purification has significant health and dietary implications, particularly for those managing specific medical conditions. Individuals on a physician-prescribed low-sodium diet, such as those with hypertension or certain kidney conditions, benefit substantially from the reduction in sodium intake provided by RO water.
The system removes a broad range of dissolved solids, including minerals like calcium and magnesium, alongside contaminants such as lead and arsenic. This comprehensive removal results in water largely devoid of mineral content, which can affect its taste, often described as “flat.” Consumers should consider that the RO process removes both beneficial and harmful dissolved solids, though the body primarily obtains necessary minerals from food.