Removal of minerals ​

Metabolism and bioavailability of minerals in water (tap or bottled)

The inorganic minerals found in water originate from the rocks the water passes over or through during its cycle (riverbeds, percolation through the Earth’s mineral layers, etc.).

These inorganic minerals make up the “dry residues“—measured in mg/L—found in the water (determined after evaporating the water at 180°C). They consist primarily of calcium (Ca) and magnesium (Mg)—the components of limescale (which forms scale deposits when water is heated)—and, to a lesser extent, trace elements (copper, iron, zinc, selenium, silicon, fluoride, etc.).

There are two methods for measuring dry residues:

• From the water hardness in French degrees (°f) and multiply by 10 mg/L ; this yields the amount of limescale (calcium carbonate, which forms scale). For example, 36°f = 360 mg/L (360 ppm, or parts per million); dividing this figure by 80% gives 450 mg/L of dry residue.
• From water’s conductivity, measured in microsiemens (µS/cm), and apply a standard conversion factor of k = 0.64. For example, 730 µS/cm (for 36°f) × 0.64 = 467 mg/L of dry residue (this is what a TDS meter measures).

Inorganic minerals are measured in mg/L and should not be confused with pollutants, which are measured in µg/L (meaning they are 1,000 times lighter and smaller) and are not detected by TDS (Total Dissolved Solids) meters.

The body absorbs these inorganic minerals in their dissolved ionic form (i.e., electrically charged) at a rate of approximately 48%, specifically:

• Between 37% and 46% for Ca (absorption comparable to that of milk)
• Between 52% and 59% for Mg

This means they are absorbed by the intestine, cross the intestinal wall, and enter the bloodstream. Once in the blood, they become available to supply the body’s cells. The ~48% of absorbed minerals are available to nourish cells and are subsequently metabolized at a rate of ~98%.

This equates to a contribution of approximately 7% of the Recommended Dietary Allowance (RDA) for Mg and 34% for Ca (depending on age, gender, water intake—assumed to be 1.5 L/person/day—and the water’s mineral content, hypothetically set at 450 mg/L, being 36°f hardness)! Consequently, the inorganic minerals present in water are highly bioavailable to our bodies—much like those found in solid foods—and thus contribute to our good health!

The inorganic minerals remaining in the intestine (~52%) are eliminated via the stool. Any excess absorbed inorganic minerals that are not metabolized—approximately 1.2% (representing 1% to 4% of the initial 48%)—are filtered by the kidneys and excreted in the urine. Therefore, there is no adverse effect on kidney function in healthy individuals, nor is there any risk of mineral overload. In fact, water rich in Ca and Mg actually has a protective effect against kidney stones!