Calcium
Cities measured
87
Detected in
87 / 87
Highest
148 mg/L — Rome
Overview
Calcium is the most abundant mineral in the human body. In water it dissolves from limestone, chalk, and dolomite. Stockholm's granite-source water has relatively low calcium (soft water) compared to cities drawing from limestone aquifers.
Health Relevance
Adequate calcium supports bone density, nerve function, and muscle contraction. Some epidemiological studies associate higher water calcium with reduced cardiovascular mortality and lower colorectal cancer risk. Drinking water typically provides 5–20% of daily calcium intake.
Regulatory Limits
Drinking Water Directive 2020/2184
No EU regulatory limit.
Controversy & Contested Science
Scandinavian epidemiological studies in the 1960s–80s found cardiovascular mortality gradients correlated with water hardness. The WHO 2006 assessment concluded evidence was 'suggestive but not conclusive' and recommended against removing calcium from drinking water. When cities soften water for infrastructure reasons, they often remineralise specifically to restore calcium — but the optimal range remains disputed. Some cardiologists argue for formal 'hard water' policies as a public health measure.
Note
The word 'calcium' derives from the Latin 'calx', meaning lime. The element was first isolated by Humphry Davy in 1808.