It depends on the spring source. Labels usually show magnesium as mg/L, so multiply by the bottle volume. For example, if a water has 50 mg/L magnesium, a 200 ml bottle provides ~10 mg and a 500 ml bottle provides ~25 mg. Some waters contain under 10 mg/L, while others exceed 100 mg/L. Sodium and bicarbonate levels also vary and may matter for people with hypertension or kidney concerns. Mineral water can contribute to intake but rarely provides “supplement-like” doses, so diet should remain the main strategy. If you drink it regularly, noting the label values can be a practical tracking method.