Understanding Magnesium in Your Water
Yes, you can get magnesium from drinking water, but the amount is highly variable and depends on the water's source and treatment. Magnesium, along with calcium, is one of the primary minerals responsible for water 'hardness'. As rainwater travels through soil and rock, such as limestone, it dissolves naturally occurring minerals, carrying them into aquifers and surface water supplies. In some areas, water with a high mineral content—often called 'hard water'—can be a surprisingly good source of dietary magnesium.
Factors Affecting Water's Magnesium Content
The concentration of magnesium in water isn't constant. Several geological and environmental factors play a role:
- Source Geology: Water that has flowed through magnesium-rich rock formations, like dolomite, will naturally have a higher concentration.
- Agricultural Runoff: Areas with heavy agricultural activity and certain drainage systems can have different mineral levels in their water supply.
- Treatment Processes: Water treatment methods, especially softening via ion exchange, can intentionally remove magnesium from the water and replace it with sodium.
- Seasonal Variations: The time of year and weather patterns can affect water flow and mineral concentrations.
- Bottled vs. Tap: Bottled mineral water often has its mineral content specified on the label, and it can be a reliable source. The magnesium in tap water varies by location, and a consumer would need a water quality report to know the exact amount.
Bioavailability: Water vs. Food and Supplements
One common question is how well the body absorbs magnesium from water compared to food or supplements. Research has shown that magnesium from mineral water is highly bioavailable and readily absorbed. This is because the magnesium is already in a dissolved, ionic state, which is easily taken up by the body. In fact, some studies have found the bioavailability from mineral water to be comparable to or even better than some dietary supplements. Some food sources, like whole grains, contain phytic acid which can bind to minerals and slightly reduce absorption.
Contribution to Your Daily Magnesium Intake
While drinking water can contribute to your daily magnesium, it typically isn't the sole source. Your dietary intake, from foods like green leafy vegetables, nuts, and legumes, remains the primary source. However, water can make a significant supplemental contribution, especially for those with low dietary intake or in areas with hard water. In areas with very high magnesium concentrations, drinking the recommended daily water amount could supply a substantial percentage of your needs. The USDA has reported that assuming a 2-liter daily intake, tap water could provide approximately 5% of the Daily Value for magnesium. This percentage can be significantly higher with certain mineral waters.
How Water Softeners Affect Your Magnesium
Water softeners use an ion exchange process that removes calcium and magnesium ions and replaces them with sodium or potassium ions. While this is beneficial for reducing scale buildup in appliances and pipes, it effectively removes the beneficial magnesium from your drinking water. If you use a water softener, it's important to be aware that your water no longer contributes to your magnesium intake. Some systems can be configured to only soften hot water, leaving the cold drinking water mineral-rich.
Comparison of Magnesium Content by Water Source
| Water Source | Typical Magnesium Content (mg/L) | Notable Characteristics |
|---|---|---|
| Tap Water | 1 to 120 mg/L (highly variable) | Dependent on regional geology and municipal treatment; can be hard or soft. |
| Bottled Mineral Water | 50 to >150 mg/L (labeled) | Mineral content is often specified; some brands are exceptionally rich in magnesium. |
| Home Filtered Water (RO) | Very low, as reverse osmosis removes most minerals | Requires a remineralization filter to add beneficial minerals back in. |
| Well Water | Up to 150 mg/L (variable by well) | Content is highly dependent on the local groundwater geology. |
Conclusion
In summary, you can indeed get magnesium from drinking water, and for many people, especially those living in hard water areas, it can provide a valuable, calorie-free supplement to their dietary intake. The amount of magnesium delivered by water is not guaranteed and varies significantly depending on the source. While mineral water provides a reliable, labeled source, the magnesium content of tap water depends on local geology and water treatment processes. If you rely on a water softener, you should know that you are likely removing this potential benefit. Ultimately, drinking water, combined with a balanced diet rich in nuts, seeds, and leafy greens, can be a supportive part of a healthy magnesium intake strategy. For those concerned about their intake, checking a local water quality report or opting for a mineral-rich bottled water can provide more definitive information. For more information on dietary minerals, visit the National Institutes of Health (NIH) Office of Dietary Supplements website at https://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/.
