Magnesium, Hard Water, and Health

The risk relationship between hard water and reduced cardiovascular disease is well known, but it’s the magnesium portion of the hardness that accounts for most of the beneficial effect. Most Americans consume less than the optimal daily amount of magnesium recommended for good health. Drinking water can be an important contributor, and the uptake of magnesium from drinking water is more efficient than from most dietary components. Even a small (~10 mg/L) consistent lifetime contribution from water can be an important supplement as we age.

Approximately half of the US population has been shown to consume less than the daily requirement of magnesium from foods (USDA & HHS 2015). Drinking water can be a lifetime contributor of supplemental magnesium to one’s total daily intake depending on the source water composition and the treatment it has received.


For magnesium, US levels are 330-350 mg/day for adult males, 255-265 mg/day for adult females, and 290-335 mg/day during pregnancy (IOM 2014). Dairy and water are among the most efficient uptake sources. Magnesium is chelated as the central atom in chlorophyll, so it is present in all green plants (Rosanoff 2013). Some 75% of leaf magnesium is involved in protein synthesis, and 15-20% of total magnesium is associated with chlorophyll pigments, acting mainly as a co-factor of a series of enzymes involved in photosynthetic carbon fixation and metabolism (Guo et al. 2016). Most deionized bottled waters sold in the United States contain little or no magnesium (NIH 2016). Magnesium-rich mineral water could make a valuable contribution to meeting an individual’s magnesium requirement (Sabatier et al. 2002).

Overall, 56% of drinking water volume was from tap water, while bottled water provided 44% (Drewnowski et al. 2013).

Numerous diseases and disorders have been related to inadequate magnesium levels from clinical and epidemiological studies. Magnesium deficiency can cause or exacerbate numerous diseases, including cardiovascular disease, hypertension, and diabetes (Costello et al. 2016).

Magnesium is necessary for DNA synthesis; maintaining bone mineral density; and protein, carbohydrate, and fat metabolism (Romani 2013). Hundreds of magnesium-dependent enzymes are involved in phosphorylation kinases that transfer a phosphate group to the recipient small organic molecule. Kinases regulate cell-cycle growth and apoptosis (programmed cell death), in which the kinases switch on inactive molecules to functional ones.

A large number of studies have investigated the potential health effects of hardness in drinking water. Many found an inverse relationship between water hardness and cardiovascular mortality (higher hardness is associated with lower mortality). It has now been concluded that if there is a benefit of reduced cardiovascular mortality, it is associated specifically with the magnesium content rather than hardness per se. All five case-control studies showed the same inverse trend of lower risk of cardiovascular mortality and magnesium in drinking water, especially at levels greater than 5 mg/L. They included seven case-control studies and three cohort studies of acceptable quality investigating calcium or magnesium and cardiovascular disease or mortality with a total of 77,821 cases. These case-control and cohort studies were much more rigorous than ecologic studies.

On the basis of the case-control and cohort studies that were analyzed, the meta-analysis concluded that the drinking water level of magnesium was significantly and inversely associated with coronary heart disease mortality, particularly in the European populations that were studied.


The consensus document made these conclusions, among others:

Consumption of hard water is associated with a somewhat lowered risk of cardiovascular disease was probably valid, and magnesium was the more likely contributor of those benefits.

Demineralized and corrosive drinking water should be stabilized where possible with additives that will increase or reestablish calcium and magnesium levels.

Water utilities are encouraged to periodically analyze their waters for calcium, magnesium, and trace elements to help assess trends and conduct future epidemiologic studies.

Guidelines for Drinking-Water Quality, the WHO should consider the beneficial roles of nutrient minerals including water hardness characteristics.

Most people in the United States are consuming less than the estimated requirement of magnesium. Drinking water can provide a baseline lifetime contribution to dietary magnesium intake. Magnesium from plant-derived food is less efficiently absorbed than from dairy and water. Numerous adverse health effects have associations with inadequate magnesium levels. There are several case-control and cohort epidemiological studies that indicate beneficial effects of reduced cardiovascular mortality associated levels of magnesium in drinking water.