Water filtration is a physical or chemical process designed to remove impurities from a water supply. The central goal of these systems is to eliminate contaminants that can affect health, taste, or odor, which include chemicals, biological agents, and dissolved solids. The question of whether filtration removes minerals depends entirely on the specific technology employed. Certain filtration methods are highly selective, leaving beneficial compounds untouched, while others are non-selective, stripping the water of almost all dissolved substances. This variability means filtration can range from simply polishing the water’s taste to creating near-pure H₂O.
Categorizing Minerals in Drinking Water
The term “minerals” in water refers to a diverse collection of inorganic substances, broadly grouped based on their chemical and health properties. These dissolved ions originate from water passing over rocks and soil in its natural cycle.
Hardness Minerals
This category is primarily composed of positively charged calcium and magnesium ions. These compounds do not pose a health risk but are responsible for the scale buildup in plumbing and appliances, defining “hard water.”
Essential Trace Minerals
This group includes small amounts of copper, iron, zinc, and selenium, which the human body utilizes for various functions.
Contaminants
This medically significant category includes inorganic substances that are toxic even in trace amounts, such as heavy metals like lead, arsenic, and cadmium. Effective water treatment must selectively target and remove these harmful contaminants while ideally leaving beneficial or harmless minerals present.
Impact of Common Filtration Technologies
The mechanism used in a filtration system dictates which categories of minerals are removed and to what extent. Understanding the underlying science of each technology clarifies the resulting mineral content of the treated water.
Activated Carbon Filters
These filters, frequently found in pitcher filters and refrigerator units, work primarily through adsorption. Organic compounds and chemicals like chlorine physically adhere to the porous surface area of the carbon material. Carbon filters are highly effective at improving taste, odor, and removing volatile organic compounds. However, they are not designed to attract or trap dissolved inorganic salts or minerals like calcium and magnesium. Consequently, carbon filtration typically leaves the majority of the water’s natural mineral content virtually unchanged.
Reverse Osmosis (RO) and Distillation
These systems employ non-selective purification methods. RO uses high pressure to force water molecules through a semi-permeable membrane with extremely small pores. This membrane physically blocks nearly all dissolved solids, including both beneficial minerals and undesirable contaminants, leading to a significant reduction in the water’s Total Dissolved Solids (TDS) content. Distillation achieves a similar outcome by boiling the water into steam, which leaves all non-volatile dissolved solids behind before condensing the pure vapor back into liquid form. Both RO and distillation produce water that is nearly devoid of all dissolved minerals.
Ion Exchange Systems
A different approach is taken by Ion Exchange systems, most commonly used in household water softeners. These systems are highly selective, designed specifically to address hard water. The process involves passing water through a bed of resin beads that chemically exchange the hardness ions (calcium and magnesium) for non-hardness ions, typically sodium or potassium. While this process removes the hardness minerals, it replaces them with another dissolved solid, meaning the overall TDS level may not drop significantly, but the composition changes entirely.
Nutritional Significance of Water Minerals
The widespread use of non-selective filters like reverse osmosis has raised consumer concerns about the health implications of drinking demineralized water. However, the primary source of essential minerals for the human body is a balanced diet of foods, not water. Dairy products, nuts, seeds, and leafy greens are the major contributors to the daily intake of minerals like calcium and magnesium. The World Health Organization (WHO) has not established a health-based minimum guideline for Total Dissolved Solids in drinking water. The human body has sophisticated homeostatic mechanisms that regulate mineral concentrations, effectively managing the intake of low-TDS water for most healthy individuals. While some waterborne minerals are highly bioavailable, the trace amounts present in most tap water are generally insufficient to fulfill daily nutritional requirements. The main drawback of extremely low-TDS water, such as that produced by RO or distillation, is often its flat or insipid taste. For this reason, some consumers opt for post-filtration remineralization, which involves introducing a small, controlled amount of food-grade minerals back into the purified water stream. Water’s primary physiological function is hydration, and it should not be relied upon as a substitute for mineral intake from food.