Reverse osmosis (RO) is a highly effective water purification method that removes a wide spectrum of impurities, providing water of exceptional clarity. This process involves forcing water through an extremely fine, semipermeable membrane to filter out contaminants such as heavy metals, chemical pollutants, and pathogens. While celebrated for its ability to produce clean drinking water, the process also strips away nearly all Total Dissolved Solids (TDS). This outcome leads to a common question: is the resulting demineralized water healthy, and is it necessary to add minerals back for long-term well-being? This article explores how RO alters water composition and addresses the scientific rationale behind remineralization.
How Reverse Osmosis Alters Water Composition
The reverse osmosis process works by applying pressure to push water molecules through a specialized membrane, which acts as a molecular sieve. This membrane is so fine that it allows only water molecules to pass, effectively blocking larger dissolved particles and separating the purified water from the concentrated stream of rejected substances.
This filtration mechanism is indiscriminate toward dissolved solids, meaning it removes both harmful contaminants and naturally occurring minerals. Substances like calcium, magnesium, and sodium are filtered out with a rejection rate often exceeding 95%. The result is water that is nearly pure H₂O, frequently described as “demineralized” due to its extremely low mineral content.
The TDS level of water treated by an RO system can drop to less than 10 milligrams per liter (mg/L). While this low TDS indicates exceptional purity from contaminants, it also signifies the water’s lack of beneficial mineral compounds.
Essential Minerals and Health Concerns
The minerals removed by reverse osmosis, particularly calcium and magnesium, have recognized biological functions important for human health. Calcium is necessary for skeletal strength, nerve signal transmission, and muscle contraction, including the heartbeat. Magnesium is involved in hundreds of enzymatic reactions, supporting energy production, protein synthesis, and proper nerve and muscle function.
The World Health Organization (WHO) has noted that drinking water low in these elements may not be ideal for long-term consumption. The WHO suggests minimum levels for drinking water, recommending a TDS concentration of at least 150-300 mg/L, with minimum targets of 20 mg/L for calcium and 10 mg/L for magnesium. While most people obtain these nutrients from food, waterborne minerals are more easily absorbed by the body in their dissolved, ionic form.
For individuals with diets low in these minerals, or for certain populations like children and pregnant people, the contribution from drinking water can be significant. Cooking with demineralized water can also leach minerals from foods, with studies showing losses of calcium and magnesium potentially reaching 60% or more from cooked vegetables. The decision to remineralize is often based on restoring this beneficial supplemental intake and mitigating potential long-term effects.
Simple Ways to Restore Mineral Content
For consumers who choose to enhance their reverse osmosis water, several practical methods exist to reintroduce beneficial minerals. The most convenient method is installing a dedicated remineralization cartridge as the final stage of the RO system. These inline filters typically contain mineral media, such as calcium carbonate or magnesium oxide, that slowly dissolve into the purified water as it passes through.
Another flexible option is the use of concentrated mineral drops, which are liquid blends of trace minerals and electrolytes. These drops can be added to individual glasses or pitchers of RO water, offering complete control over the final mineral concentration. This customization allows users to adjust the taste and mineral dose according to personal preference.
For a simple, do-it-yourself approach, adding a small pinch of high-quality mineral-rich salt, such as Himalayan or Celtic sea salt, can slightly raise the mineral and electrolyte content. While this method is inexpensive, it provides less precise control over the exact mineral profile compared to engineered cartridges or drops. Periodically testing the water’s TDS level post-remineralization is a helpful practice to ensure the desired concentration is maintained.