Reverse Osmosis Deionization (RODI) water is a highly purified form of water created through a rigorous, multi-stage filtration process. This method combines two water treatment technologies to produce water with near-zero total dissolved solids (TDS), making it chemically pure H₂O. RODI water is often used in specialized applications like laboratory work, manufacturing, and for sensitive marine aquariums where absolute purity is required. The process removes virtually all contaminants, raising questions about its suitability for human consumption.
Understanding Reverse Osmosis and Deionization
The creation of RODI water begins with reverse osmosis (RO), a physical filtration method that forces water through a semipermeable membrane under pressure. This membrane acts as a barrier, rejecting between 90% and 99% of dissolved solids, salts, large organic molecules, and heavy metals. The RO stage is highly effective at removing the bulk of contaminants.
However, the RO membrane may allow a small percentage of tiny, charged particles, or ions, to pass through. The deionization (DI) stage is introduced as a final polishing step. The DI process uses specialized ion-exchange resins that chemically exchange positive hydrogen (H⁺) and negative hydroxyl (OH⁻) ions for any remaining dissolved mineral ions, such as sodium, calcium, nitrates, and phosphates. The combination of RO and DI results in water virtually devoid of everything except water molecules, achieving a purity level close to 99.9% contaminant removal and a TDS reading of zero.
Health Implications of Drinking Demineralized Water
While RODI water is technically clean, its long-term consumption is generally not recommended because it lacks essential minerals. The World Health Organization (WHO) has raised concerns regarding the regular intake of demineralized water due to potential adverse health effects. This water is missing beneficial minerals like calcium and magnesium, which are important for various bodily functions.
Drinking water is a small but steady source of these nutrients, and removing them entirely can contribute to low intake, especially if a person’s diet is already deficient. Furthermore, ultra-pure water is highly aggressive and seeks to regain its mineral balance. This means that if used for cooking, it can leach minerals from foods, further reducing the nutritional value of the meal.
Long-term exclusive consumption of water with extremely low mineral content may compromise the body’s mineral and water metabolism. In some cases, consuming demineralized water has been associated with an increased risk of mineral deficiencies and potential electrolyte imbalances. Symptoms of this imbalance can include tiredness, weakness, headache, and in more severe, acute cases, muscular cramping. The lack of dissolved solids also gives RODI water a flat, dull, or poor taste, which may affect palatability and discourage adequate hydration.
Strategies for Making RODI Water Suitable for Consumption
For individuals who use a purification system that produces RODI water, it is necessary to reintroduce minerals before drinking it. The most convenient solution is to use a dedicated remineralization cartridge added to the filtration system. These cartridges typically contain a mix of minerals, such as calcium and magnesium compounds, which slowly dissolve back into the purified water to achieve a balanced total dissolved solids level.
A more manual approach involves adding concentrated mineral drops or trace electrolyte solutions to the water by the glass or pitcher. This allows for precise control over the mineral concentration, adjustable based on personal preference or dietary needs. Some users also opt for adding a small pinch of mineral-rich salt, such as Himalayan salt, though this method is less precise for consistent dosing.
RO vs. RODI for Home Use
For most home drinking water applications, the deionization step is often unnecessary, and a standard Reverse Osmosis system alone is sufficient. RO water removes the vast majority of contaminants but may retain trace amounts of ions. Using a remineralization stage in an RO system ensures that while contaminants are removed, the resulting water retains the beneficial minerals that support overall health.