RO systems are widely used to improve drinking water quality by removing a broad spectrum of contaminants. This effectiveness often leads users to question what happens to naturally occurring substances, particularly beneficial minerals. This article explores the science behind RO filtration to answer that question and address the practical implications of drinking demineralized water.
The Mechanism of Reverse Osmosis Filtration
Reverse osmosis (RO) is a filtration method that works by overcoming a natural process known as osmosis. Osmosis is the movement of water molecules across a semipermeable membrane from low to high solute concentration. In an RO system, external pressure is applied to the highly concentrated side, forcing the water molecules to move in the opposite direction.
This applied pressure pushes the water through a synthetic semipermeable membrane, leaving behind larger molecules and dissolved solids. The membrane is engineered with extremely fine pores, typically around 0.0001 micron. This physical barrier separates the water stream into two paths: the purified water, called the permeate, and the concentrated waste stream that carries the rejected substances to the drain.
Efficiency of Mineral Removal and Water Purity
Reverse osmosis is designed to remove dissolved minerals. The system’s effectiveness is measured by its ability to reduce Total Dissolved Solids (TDS), which includes inorganic salts, organic matter, and minerals. High-quality RO membranes achieve a remarkable reduction in TDS, often removing between 95% and 99% of these dissolved substances from the source water.
This process effectively removes divalent ions like calcium and magnesium, which are the components of water hardness. It also strips away monovalent ions such as sodium and fluoride, along with heavy metals like lead and arsenic. The resulting product water is highly purified, containing very low levels of dissolved solids, often falling into a range of 10 to 50 parts per million (PPM). This clean water is referred to as demineralized or “soft” water due to its near-total lack of mineral content.
Health Implications of Demineralized Water
While the purity of RO water is a benefit, its lack of minerals has led to discussions regarding long-term health effects. Demineralized water, by definition, contains little to none of the minerals that contribute to human dietary intake, such as calcium and magnesium. The World Health Organization (WHO) has noted that water with a very low mineral content is not considered an ideal source of drinking water for regular consumption.
The concern is that the consumption of demineralized water may not provide adequate levels of these beneficial nutrients. Some studies suggest that a lack of minerals in drinking water may correlate with a higher risk of certain health issues, such as cardiovascular disease. The WHO suggests that drinking water should ideally have a minimum TDS concentration of 100 mg/L, including specific minimums for calcium and magnesium.
To address the absence of minerals, many users choose to implement a process called remineralization. These techniques ensure the water maintains its purified state while restoring a more pleasant taste and reintroducing trace elements for nutritional balance.
Methods of Remineralization
The most convenient method is integrating a remineralization cartridge as the final stage of the RO system. This automatically reintroduces a balanced blend of beneficial minerals like calcium and magnesium.
Another practical solution involves using concentrated mineral drops, which are liquid blends added manually to a glass or pitcher of water.
Some consumers opt for alkaline water pitchers, which contain media that reintroduces minerals and simultaneously raises the water’s pH level.
A simple, do-it-yourself method involves adding a pinch of mineral-rich salts, such as Himalayan salt, to the water, though controlling the exact concentration is difficult.