Mineral water is a natural source of hydration that does not cause dehydration for the vast majority of healthy consumers. This common concern stems from a misunderstanding of how the body processes the mineral content in water. For a substance to be dehydrating, it must contain a concentration of solutes significantly higher than the body’s own fluids, which is not the case with commercially available mineral water. Mineral water, whether still or sparkling, contributes positively to daily fluid intake, supporting overall health and fluid balance.
Understanding Hydration and Osmotic Balance
Hydration is a state of fluid balance where the water taken into the body equals the water lost through processes like urination, breathing, and sweating. Dehydration occurs when the body loses proportionately more water than it does solutes, leading to an increase in the concentration of salts and minerals in the blood plasma. This concentration is measured as plasma osmolality.
The body maintains this delicate balance through a process called osmoregulation, which controls the movement of water across semi-permeable cell membranes. Water moves by osmosis from areas of low solute concentration to areas of high solute concentration. If the fluid outside a cell is too concentrated (hypertonic), water leaves the cell; if it is too dilute (hypotonic), water enters the cell.
The body tightly regulates the osmolality of its fluids to prevent cells from shrinking or swelling. When the blood’s solute concentration rises too high, osmoreceptors in the brain trigger the sensation of thirst and prompt the release of anti-diuretic hormone (ADH) to conserve water. Drinking water, even mineral water, helps to dilute the plasma and restore the proper osmotic balance.
Defining Mineral Water Composition
Mineral water is naturally sourced from underground reservoirs, emerging with a fixed and stable composition of dissolved solids. These natural geological sources enrich the water with various inorganic salts, including calcium, magnesium, sulfates, and sodium. The mineral content is measured using Total Dissolved Solids (TDS), typically expressed in milligrams per liter (mg/L).
To be classified as mineral water, the water must generally have a minimum TDS of 250 mg/L. Many popular brands fall in the medium range of 250 to 800 mg/L, though some specialized waters occasionally exceed 1,500 mg/L. This naturally occurring mineral load distinguishes it from purified or tap water, which often has a much lower TDS.
Why Mineral Water Does Not Cause Dehydration
Mineral water is fundamentally hydrating because its solvent, water, is absorbed into the bloodstream across the intestinal wall. The concentration of solutes in even highly mineralized water is negligible when compared to the osmolality of human blood plasma, which is approximately 9,000 mg/L. A liquid must be significantly hypertonic relative to the body’s fluids to draw water out of the cells and cause dehydration.
For instance, seawater has a TDS of over 25,000 mg/L, which is why drinking it causes severe dehydration as the body attempts to excrete the excessive salt load. Mineral water, even at 1,500 mg/L TDS, is still hypotonic or close to isotonic relative to the body’s internal environment. Therefore, it is absorbed efficiently, contributing to fluid volume without triggering the osmotic shift that leads to dehydration.
Once absorbed, the kidneys efficiently manage the slight excess of minerals, excreting them in the urine while conserving fluid volume. This process does not require the body to sacrifice a net amount of water. In fact, the small electrolyte content in mineral water can sometimes make it more effective for rehydration than pure water.
Situations Where High Mineral Intake Requires Caution
While mineral water is safe for the average person, individuals with certain health conditions may need to monitor their mineral intake. People with severe kidney impairment, such as chronic kidney disease, may struggle to excrete excess minerals like potassium and sodium. High concentrations of these electrolytes could accumulate, leading to health complications.
Individuals on a strict sodium-restricted diet, often due to hypertension, should also check the label of their chosen mineral water. Some high-mineral waters contain sodium levels that could contribute significantly to their daily intake. Consulting a healthcare provider about the sodium content is a prudent measure for those managing specific dietary restrictions.