Magnesium
Cities measured
87
Detected in
87 / 87
Highest
38 mg/L — Karachi
Overview
Magnesium is a cofactor for 300+ enzymatic reactions. It dissolves from dolomite and silicate rocks. Like calcium, it contributes to total water hardness. Stockholm's soft granite-source water has lower magnesium than hard-water cities.
Health Relevance
Magnesium deficiency is linked to hypertension, cardiac arrhythmias, type 2 diabetes, and muscle cramps. Drinking water can contribute meaningfully to daily intake — especially for populations with magnesium-poor diets high in processed foods.
Regulatory Limits
Drinking Water Directive 2020/2184
No EU regulatory limit.
Controversy & Contested Science
The European Magnesium Research Society has repeatedly called on water authorities to set a minimum magnesium concentration (~10 mg/L) in drinking water, citing studies linking low water magnesium to sudden cardiac death. Water utilities have resisted, arguing dietary supplementation is more practical. Critics note this framing may reflect the cost of remineralisation infrastructure rather than genuine evidence assessment. Some researchers describe this as 'a missed public health opportunity costing thousands of preventable cardiac deaths annually.'