Since 2000, the WHO (World Health Organisation) has been investigating the evidence behind the hypothesis that minerals (specifically calcium and magnesium) in drinking water may be beneficial to cardiovascular disease (Click here for summary of the activity). The current position of the WHO is identified in the latest 2011 edition (fourth) of the WHO Guidelines for Drinking-water Quality which conclude:
“Although there is evidence from epidemiological studies for a protective effect of magnesium or hardness on cardiovascular mortality, the evidence is being debated and does not prove causality. Further studies are being conducted. There are insufficient data to suggest either minimum or maximum concentrations of minerals at this time, as adequate intake will depend on a range of other factors. Therefore, no guideline values are proposed.”
The position of the UKWTA (link to report) is that the evidence for a potential health benefit from water hardness is very weak and confined to magnesium content, for which the contribution to dietary intake would normally be trivial. The justification for any informative action is, at this stage, highly questionable and, when balanced against the benefits of soft (or softened) water, and against the benefits of optimum hydration, positive statement or action is inappropriate unless and until there are definitive conclusions from the recommended research.