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. Magnesium is important in hundreds of biochemical processes, and adult daily requirements are approximately 300–350 mg/day. Most Americans consume less than the optimal daily amount of magnesium recommended for good health. Although diet is the major source of magnesium, drinking water can be an important contributor, and the uptake of magnesium from drinking water is more efficient than from most dietary components except milk/dairy. Dairy intake tends to decline with age, so even a small (~10 mg/L) consistent lifetime contribution from water can be an important supplement as we age. Bottled waters and naturally soft and softened waters tend to have little or no magnesium.