Reverse osmosis (RO) is a water purification method that utilizes pressure to push water through a very fine, semipermeable membrane. This process removes a broad spectrum of contaminants, making the resulting water safer to drink than untreated tap water. RO technology can eliminate up to 99% of dissolved solids and impurities. The primary safety question centers on what RO leaves behind: a nearly pure, demineralized water source. This article explores the filtration mechanism, health, and maintenance considerations.
How Reverse Osmosis Works
RO systems apply external pressure to contaminated water, forcing water molecules through a semipermeable membrane. This membrane has extremely small pores that allow water molecules to pass through while rejecting larger molecules, ions, and particles.
The process separates the feed water into two streams: the purified water (permeate) and the concentrated stream of rejected contaminants (brine), which is flushed down the drain. Before reaching the core membrane, water passes through pre-filters, such as sediment and carbon filters. Pre-filters remove larger debris and substances like chlorine that could damage the membrane.
The membrane is effective at removing a wide range of dissolved inorganic solids and contaminants. These include salts, heavy metals, nitrates, fluoride, and microorganisms. The microscopic pore size enables this high degree of contaminant removal, resulting in water with a very low total dissolved solids (TDS) content.
The Health Implications of Demineralized Water
The RO membrane removes almost everything, including beneficial minerals like calcium and magnesium, resulting in demineralized water. While these minerals are mainly acquired through diet, their removal has led to a safety debate. The World Health Organization (WHO) notes that consuming water with very low mineral content long-term may not be suitable, especially if the diet is already deficient.
A lack of minerals in drinking water increases the risk of nutrient deficiency. Calcium and magnesium are important for bone health and cardiovascular function. Low-mineral water could potentially leach minerals from the body or from food cooked in it. For individuals with a varied diet, the mineral content of water is less significant, as food provides the majority of mineral intake. However, relying solely on demineralized water may pose a greater risk of mineral imbalance for sensitive populations, such as children or those with poor nutrition.
Ensuring Optimal Safety Post-Filtration
To address the loss of beneficial minerals, they are commonly reintroduced into the water after the RO process. The most convenient method is using a remineralization filter, often an added stage in the RO system. These filters contain media like calcium carbonate or magnesium oxide, which dissolve back into the purified water. These cartridges restore a balanced mineral profile and improve the water’s taste, which can be “flat” when demineralized.
Manual Remineralization
Consumers can manually add trace mineral drops or a pinch of mineral-rich salt directly to the water. This allows for a customized mineral dosage, but requires consistent effort.
System Maintenance
RO system safety relies on routine maintenance. This includes the timely replacement of pre-filters and the membrane according to the manufacturer’s schedule. Regular sanitization is necessary to prevent bacterial growth within the system’s carbon filters or the storage tank, which can compromise water quality.